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J B Hicks

Publications and source records attributed to J B Hicks.

48 records · Page 3Linked to original sources
PubMed1980

Evidence for a physical interaction between the transposed and the substituted sequences during mating type gene transposition in yeast.

Mating type switches in the yeast Saccharomyces cerevisiae occur by transposition of a replica of the "source" unexpressed loci HML and HMR to the mating type locus (MAT). The incoming information replaces previously expressed DNA, resulting in an interconversion of MAT alleles. A strain of genotype HML alpha/HML alpha MAT alpha/mata-missense HMR alpha/hmra-nonsense HO/ho generates cells with the genotype HML alpha/HML alpha MAT alpha/MAT a HMR alpha/hmra-nonsense HO/ho; that is, wild-type MATa+ recombinants are produced efficiently by a strain in which the incoming a information and the resident mata allele bear different mutations. Production of the wild-type MATa recombinants requires the homothallism (switching) function, and the incoming a information and the resident mata allele must bear different mutations. This result is consistent with the formation of a heteroduplex between the incoming and the outgoing DNA at MAT. Thus a process of unidirectional gene conversion as a mechanism for mating type gene transposition is favored. A molecular model based on a single-strand transfer is proposed. Results also favor the idea that the direction of switching is controlled by cell's mating phenotype rather than by the genetic content of MAT.

Alleles↗
PubMed1980

Replication and recombination functions associated with the yeast plasmid, 2 mu circle.

By examining both the transformation efficiency of yeast of various plasmids containing defined regions of the 2 mu circle genome and the characteristics of the resultant transformants, we have identified several regions of the 2 mu circle genome which are involved in 2 mu circle replication or recombination. First, by identifying those DNA fragments from the molecule which promote high frequency transformation of yeast, we have localized the origin of replication to a sequence partially within the large unique region, which, as determined by subsequent deletion analysis, extends from the middle of the inverted repeat region into the contiguous unique region. Second, by examining the relative efficiency of replication in yeast of hybrid plasmids containing either the entire 2 mu circle genome or a fragment of 2 mu circle encompassing the origin of replication, we have determined that efficient use of the 2 mu circle origin requires some function or functions encoded in the molecule at a site away from the origin. Third, by examining the ability of a mutant 2 mu circle molecule to undergo intramolecular recombination in yeast, we have identified a 2 mu circle gene which codes for a product required for this process.

Base Sequence↗
PubMed1980

Structure and organization of transposable mating type cassettes in Saccharomyces yeasts.

Cell type in Saccharomyces yeasts is regulated by two transposable blocks of DNA, the a and alpha cassettes. There are three loci where either cassette can exist. At the HML and HMR loci the cassettes are not expressed. The cassette at the MAT locus is expressed and controls the cell type. Changes of cell type involve transposition-substitution of cassettes from HML or HMR into MAT. We recently reported the molecular cloning of the alpha cassette at the HML locus, HML alpha, and showed that it contained sequences homologous to HMR and MAT. Using HML alpha as a hybridization probe, we have isolated HMLa, HMR alpha, HMRa, MAT alpha, and MATa. Heteroduplex analysis and restriction endonuclease mapping studies indicate that the a and alpha cassettes differ by a substitution corresponding to about 750 base pairs in alpha and about 600 base pairs in a. The HML, HMR, and MAT loci have regions of homology flanking the position of the a versus alpha substitution. We have used specific chromosome rearrangements fusing MAT and HML and MAT with HMR to orient the cloned sequences on the genetic map and have found that all three genes have the same left-to-right polarity on the chromosome.

Alleles↗
PubMed1980

Precise mapping of the homothallism genes HML and HMR in Saccharomyces cerevisiae.

The HML and HMR loci carry unexpressed copies of MATa and MAT alpha information, and a replica of that information is transposed to MAT during mating-type interchange in Saccharomyces yeasts. A negative control mechanism keeps silent the information located at the HML and HMR loci. We mapped these loci by constructing strains in which these loci are expressed. In these strains, the mating type of the segregants is dependent upon the allele at HML and HMR. This novel approach is independent of their switching function. HML is located on the left arm of chromosome III distal to his4 by about 26.8 centimorgans (cM). HMR maps on the right arm of the same chromosome distal to thr4 by about 39.8 cM and proximal to MAL2 by about 1.0 cM. The results allow the exact placement of these loci and are in accord with the observations made by Harashima and Oshima (1976).

Chromosome Mapping↗
PubMed1979

Isolation of a circular derivative of yeast chromosome III: implications for the mechanism of mating type interconversion.

We describe genetic and physical characterization of rearrangements of chromosome III which result in changes of cell type in S. cerevisiae. Two types of rearrangements were obtained as rare events which caused a change at the locus controlling cell type, MAT, associated with a recessive lethal mutation, in one case from MATalpha to MATa-lethal, and in the other case from MATa to MATalpha-lethal. The MATa-lethal mutation is a deletion on the right arm of chromosome III, which we demonstrate extends to (or near) HMalpha. We suggest this deletion removes MATalpha and activates cryptic MATa information stored in HMalpha as proposed in the cassette model of mating type interconversion. The MATalpha-lethal mutation is the result of the formation of a circular chromosome III, which we interpret to remove MATa and activate the cryptic MATalpha information stored at HMa. Strains carrying the MATalpha-lethal chromosome contain a circular chromosome of length 62.6 plus or minus 5.7 mum, which is absent in related strains. This chromosome was confirmed to be chromosome III by hybridization of specific yeast DNA fragments to supercoiled DNA obtained from MATalpha-lethal strains. The isolation of a large circular derivative of chromosome III allows correlation of genetic and physical distance based on large distances-1 centimorgan corresponds to approximately 2700 base pairs.

Chromosome Aberrations↗
PubMed1979

Transformation in yeast: development of a hybrid cloning vector and isolation of the CAN1 gene.

We have constructed a plasmid, YEp13, which when used in conjunction with transformation in yeast is a suitable vector for isolating specific yeast genes. The plasmid consists of pBR322, the LEU2 gene of yeast, and a DNA fragment containing a yeast origin of replication from 2 mu circule. We have demonstrated the utility of this cloning system by isolating the yeast gene encoding the arginine permease, CAN1, from a pool of random yeast DNA fragments inserted into YEp13.

Arginine↗
PubMed1979

A suppressor of mating-type locus mutations in Saccharomyces cerevisiae: evidence for and identification of cryptic mating-type loci.

A mutation has been identified that suppresses the mating and sporulation defects of all mutations in the mating-type loci of S. cerevisiae. This suppressor, sir1-1, restores mating ability to mat alpha 1 and mat alpha 2 mutants and restores sporulation ability to mat alpha 2 and mata1 mutants. MATa sir1-1 strains exhibit a polar budding pattern and have reduced sensitivity to alpha-factor, both properties of a/alpha diploids. Furthermore, sir1-1 allows MATa/MATa, mat alpha 1/mat alpha/, and MAT alpha/MAT alpha strains to sporulate efficiently. All actions of sir1-1 are recessive to SIR1. The ability of sir1-1 to supply all functions necessary for mating and sporulation and its effects in a cells are explained by proposing that sir1-1 allows expression of mating type loci which are ordinarily not expressed. The ability of sir1-1 to suppress the mat alpha 1-5 mutation is dependent on the HMa gene, previously identified as required for switching of mating types from a to alpha. Thus, as predicted by the cassette model, HMa is functionally equivalent to MAT alpha since it supplies functions of MAT alpha. We propose that sir1-1 is defective in a function. Sir ("Silent-information regulator"), whose role may be to regulate expression of HMa and HM alpha.

Chromosome Mapping↗
PubMed1978

Transformation of yeast.

A stable leu2- yeast strain has been transformed to LEU2+ by using a chimeric ColE1 plasmid carrying the yeast leu2 gene. We have used recently developed hybridization and restriction endonuclease mapping techniques to demonstrate directly the presence of the transforming DNA in the yeast genome and also to determine the arrangement of the sequences that were introduced. These studies show that ColE1 DNA together with the yeast sequences can integrate into the yeast chromosomes. This integration may be additive or substitutive. The bacterial plasmid sequences, once integrated, behave as a simple Mendelian element. In addition, we have determined the genetic linkage relationships for each newly introduced LEU2+ allele with the original leu2- allele. These studies show that the transforming squences integrate not only in the leu2 region but also in several other chromosomal locations.

Alcohol Oxidoreductases↗