Molec. gen. Genet. 179, 703-705 (1980) © by Springer-Verlag 1980

Short Communication

The RAD52 Gene Is Not Required for the Function of the DELl Mutator Gene in Saccharomyces cerevisiae Susan W. Liebman and Karen M. Downs Department of Biological Sciences, University of Illinois at Chicago Circle, Box 4348, Chicago, Illinois 60680, USA

Summary. The D E L l mutator in Saccharomyces cerevisiae leads to the formation of deletions adjacent to itself (Liebman et al. 1979). Here we show that the frequency of these D E L l - p r o m o t e d deletions is not altered by the presence of the recombinationdeficient mutation, rad52-1. This indicates that generalized recombination is not required for the formation of deletions in D E L l yeast strains.

During vegetative growth, the recently described D E L l mutator gene (Liebman et al. 1979) of Saccharomyces cerevisiae causes a high rate (10 -5 to 10 - 6 per cell division) of multisite mutations that encompass three genes adjacent to itself: CYC1, which determines the structure of iso-l-cytochrome c; R A D L which controls U.V. sensitivity; and O S M 1 , which controls osmotic sensitivity. In contrast, normal strains (dell +) do not produce such multisite mutations even after mutagenic treatments and produce all types of cycl mutants at a low rate of approximately 10 -8 to 10 9 per cell division. D E L l segregates as a single Mendelian gene and appears to be both cis- and transdominant. Using restriction enzyme analysis we have recently shown that these multisite mutations are deletions (Liebman, Shalit and Picologlou, unpublished observations). Although the mechanism of action of the D E L l mutator has not been definitively established, it is probable that the mutator contains an element that is analogous to transposable elements in bacteria. Such transposable sequences called Tyl and 6 have recently been described in yeast and copies are found in the sup4-eycl region of the chromosome (Cameron et al. 1979). Indeed, these elements have already been Offprint requests to : S.W. Liebman

implicated in the formation of deletions at the sup4 locus (Rothstein 1979). Transposable elements in bacteria are known to promote the production of deletions and to code for some trans-acting gene products involved in the transposition events (Reif and Saedler 1975; Heffron et al. 1977; Gill et al. 1978; Kleckner et al. 1979). Bacterial transposition usually does not require generalized recombination functions (Rubens et al. 1976; Cohen 1976, Kleckner 1977, Shapiro et al. 1977), although transposition of certain T n l / 3 mutants requires a functional recA gene product for the generation of normal transposition products (Arthur and Sherratt 1979). This suggests that generalized recombination enzymes can substitute for some transposon-encoded enzymes. The purpose of the present study was to determine whether generalized recombination functions are involved in the formation of multisite mutations in D E L l yeast strains. To alter recombination, we used rad52-1, a mutation that causes sensitivity to X-rays (Game and Mortimer 1974), reduces both meiotic and mitotic recombination (Game et al. 1980; Prakash et al. 1980; Malone and Esposito 1980), and prevents homothallic mating type interconversion (Malone and Esposito 1980). We therefore asked whether the R A D 5 2 gene product was required for the production of multisite mutations in D E L l strains. A D E L l CYC1 + rad52-1 strain (SL513-9A) was obtained from the meiotic progeny of a non-mutator strain, dell + c y c l - rad52-1 (LP682-1C, kindly supplied by Dr. Louise Prakash), crossed with a mutator but otherwise wild-type haploid, D E L l CYC1 + R A D 5 2 + (SL392-1 B, Liebman et al. 1979). The segregation of rad52-1 was followed by the inability of rad52-1 mutants to grow on plates containing 0.008 % methyl methanesulfonate (MMS) (Malone and Esposito 1980). The CYC1 + and c y c l - segregants were distinguished by low temperature spectroscopic examinations of whole cells since they respectively

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S.W. Liebman and K.M. Downs: The Yeast Mutator, D E L l , is RAD52-Independent

Table 1. Frequency of deletions in tad52-1 D E L l , RAD52 + D E L l and R A D 5 2 + dell + strains Strain No.

Exp. No. a

Relevant genotype

No. cells per plate after residual growth b

Av. no. resistant mutants per plate

% of resistant m u t a n t s that are cycl deletions c

v of cycl deletions

SL513-9A SL513-9A SL513-9A SL513-9A SL356-4B SL392-2B D311-3A D9I 1-2B

1 2 3 4

rad52-1 D E L l tad52-1 D E L l rad52-1 D E L l rad52-1 D E L l RAD52 + D E L l RA D52 + D E L l RAD52 + dell + RAD52 + dell +

1.5(_+0.2) x 10 v 5(_+ 3) × 106 9(_+ 1) × 106 8(_+2) × 106

124_+ 16 47_+ 8 137_+ 10 110_+ 10

64 21 53 52

6(_+2) x 10 6 3(_+2) × 10 -6 8(_+2) x 10 -6 8(_+2) × 10 -6 8 ( + 3 ) x t0 6a 3( _+2) x 10- 6 d <2.5 × 10 - l ° d < 3.3 × 10-10a

To determine the cycl deletion frequency, approximately 106 cells per plate were spread on /3-chlorolactate media (1% Bacto-yeast extract, 2% Bacto-peptone, 3% (V/V) glycerol, 2% Bacto-agar and 0.05% /~-chlorolactic acid). While the growth of normal strains is inhibited on this medium, mutations at the eycl locus, as well as mutations at a variety of other loci, result in resistance (Sherman et al. 1974) " Experiments were performed on separate subclones b Residual growth was measured by quantitatively washing cells off the plates. The n u m b e r of cells per plate increased during the first few days, but then remained constant for several days before resistant colonies began to appear ° For each experiment, approximately 100 resistant colonies were randomly selected and tested for the presence of eyel deletions. Deletions were identified as eycl, rad7 and osml triple m u t a n t s by complementation tests (Liebman et al. 1979) d Data from Liebman et al. 1979

contain and lack the characteristic absorption bands associated with iso-l-cytochrome c (Sherman and Slonimski 1964). Since the D E L l gene is linked to cycl within 6 centimorgans (Liebman et al. 1979), 94% or more of the CYC1 + segregants in the above cross also contain the D E L l mutator gene. Accordingly, we chose a CYC1 rad52-1 segregant, SL513-gA, and tried to detect the D E L l gene by measuring the cycl mutation frequency. In four independent experiments, we found that the cycl mutation frequency in SL513-9A was within the 10 .5 to 10 6 mutations per cell range established for D E L l strains (see Table 1). Furthermore, nearly all of the cycl mutants isolated were concurrently mutated at the rad7 and osml loci and were thus judged to be deletions. Since rad52-1 is an unstable gene, we verified that rad52-1 had not reverted in SL513-9A or in the cycl deletions derived from SL513-9A, by showing that they all failed to complement a tad52 tester for growth on media containing MMS. Furthermore, we verified that the rad52 mutation present in one of our cycl deletion strains affected recombination because it prevented homothallic mating type interconversion. These results demonstrate that the D E L l and rad52-1 genes are present in SL513-9A and that the phenotype of the D E L l gene was not altered by the rad52-1 mutation. Since tad52-1 drastically reduces generalized recombination, it appears that generalized recombination is not required for the formation of multisite mutations in D E L l yeast strains. This is

reminiscent of the finding that generalized recombination is neither required for transposition nor transposable element-mediated deletion in bacteria. Acknowledgements. We thank Drs. Louise Prakash and Robert

Malone for supplying us with strains and helpful advice. This work was supported by a grant from the National Science Foundation (NSF 7904584).

References Arthur A, Sherratt D (1979) Dissection of the transposition process : A transposon-encoded site-specific recombination system. Mol Gen Genet 175 : 267-274 C a m e r o n JR, Loh EY, Davis R W (1979) Evidence for transposition of dispersed repetitive D N A families in yeast. Cell 16:739751 Cohen SN (1976) Transposable genetic elements and plasmid evolution. Nature 263:731 738 G a m e J, Mortimer R (1974) A genetic study of X-ray sensitive mutants in yeast. Mutat Res 24:281-292 Game JC, Z a m b TJ, Braun RJ, Resnick M, Roth R M (1980) The role of radiation (tad) genes in meiotic recombination in yeast. Genetics 94: 51-68 Gill R, Heffron F, D o u g a n G, Falkow S (1978) Analysis of sequences transposed by complementation of two classes of transposition-deficient m u t a n t s of Tn3. J Bacteriot 136:742-756 Heffron F, Bedinger P, C h a m p o u x JJ, Falkow S (1977) Deletions affecting the transposition of an antibiotic resistance gene. Proc Natl Acad Sci U S A 74:702-706 Kleckner N (1977) Translocatable elements in procaryotes. Cell 11 : 11-23 Kleckner N, Reichardt K, Botstein D (1979) Inversions and deletions of the Salmonella chromosome generated by the translocatable tetracycline resistance element Tn 10. J Mol Biol 127 : 89115

S.W. Liebman and K.M. Downs: The Yeast Mutator, DELl, is RAD52-Independent Liebman SW, Singh A, Sherman F (1979) A mutator affecting the region of the iso-l-cytochrome c gene in yeast. Genetics 92:783 802 Malone RE, Esposito RE (1980) The RAD52 gene is required for homothallic interconversion of mating types and spontaneous mitotic recombination in yeast. Proc Natl Acad Sci USA 77 : 503-507 Prakash S, Prakash L, Burke W, Montelone BA (1980) Effects of the RAD52 gene on recombination in Saccharomyces cerevisiae. Genetics 94:31-50 Reif HJ, Saedler H (1975) IS1 is involved in deletion formation in the gal region of E. coli K 12. Mol Gen Genet 137:1758 Rothstein R (1979) Deletions of a tyrosine tRNA gene in S. cerevisiae, Cell 17:185-190 Rubens D. Heffron F, Falkow S (1976) Transposition of a plasmid deoxyribonucleic acid sequence that mediates ampicillin resis-

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tance: independence from host rec functions and orientation of insertion. J Bacteriol 128:425-434 Shapiro JA, Adhya S, Bukhari A (1977) Introduction: New pathways in the evolution of chromosome structure. In: Bukhari A, Shapiro J, Adhya S (eds) DNA insertion elements, plasmids, and episomes. Cold Spring Harbor Laboratory, Cold Spring Harbor NY, p 3 Sherman F, Slonimsky PP (i964) Respiration-deficient mutants of yeast II. Biochim. Biophys. Acta 90:1-15 Sherman F, Stewart JW, Jackson M, Gilmore RA, Parker JH (1974) Mutants of yeast defective in iso-l-cytochrome c. Genetics 77 : 255 284 Communicated

b y D. S h e r r a t t

Received July 1, 1980