Homologues of the engrailed gene from five molluscan classes

AbstractWe used the polymerase chain reaction (PCR) to amplify, clone, and sequence 10 engrailed homeodomains from 8 species in the five major molluscan classes, including the serially organized chiton (Polyplacophora) lineage. The Drosophila melanogaster gene engrailed (en) is one of several genes involved in embyonic segment polarity determination. Studies of engrailed sequence and expression in molluscs are of interest due to questions regarding the evolution and homology of segmentation in these taxa. Nucleotide and deduced amino acid sequence comparisons reflect evolutionary conservation within helices of the en homeodomain and ancient divergences in the region 3′ to the homeodomain

Alternative Mechanisms for Tn5 Transposition

Bacterial transposons are known to move to new genomic sites using either a replicative or a conservative mechanism. The behavior of transposon Tn5 is anomalous. In vitro studies indicate that it uses a conservative mechanism while in vivo results point to a replicative mechanism. To explain this anomaly, a model is presented in which the two mechanisms are not independent—as widely believed—but could represent alternate outcomes of a common transpositional pathway

Whole-Genome Sequencing of Sake Yeast Saccharomyces cerevisiae Kyokai no. 7

The term ‘sake yeast’ is generally used to indicate the Saccharomyces cerevisiae strains that possess characteristics distinct from others including the laboratory strain S288C and are well suited for sake brewery. Here, we report the draft whole-genome shotgun sequence of a commonly used diploid sake yeast strain, Kyokai no. 7 (K7). The assembled sequence of K7 was nearly identical to that of the S288C, except for several subtelomeric polymorphisms and two large inversions in K7. A survey of heterozygous bases between the homologous chromosomes revealed the presence of mosaic-like uneven distribution of heterozygosity in K7. The distribution patterns appeared to have resulted from repeated losses of heterozygosity in the ancestral lineage of K7. Analysis of genes revealed the presence of both K7-acquired and K7-lost genes, in addition to numerous others with segmentations and terminal discrepancies in comparison with those of S288C. The distribution of Ty element also largely differed in the two strains. Interestingly, two regions in chromosomes I and VII of S288C have apparently been replaced by Ty elements in K7. Sequence comparisons suggest that these gene conversions were caused by cDNA-mediated recombination of Ty elements. The present study advances our understanding of the functional and evolutionary genomics of the sake yeast

A site-specific endonuclease essential for mating-type switching in Saccharomyces cerevisiae

We have detected two site-specific endonucleases in strains of Saccharomyces cerevisiae. One endonuclease, which we call YZ endo, is present only in yeast strains that are undergoing mating-type interconversion. The site at which YZ endo cleaves corresponds to the in vivo double-strand break occurring at the mating-type locus in,yeast undergoing mating-type interconversion. YZ endo generates a site-specific double-strand break having 4-base 3′ extensions terminating in 3′ hydroxyl groups. The site of cleavage occurs in the Z1 region near the YZ junction of the mating-type locus. Mutant mating-type loci known to decrease the frequency of mating-type interconversion are correspondingly poor substrates for YZ endo in vitro. In vitro analysis of a number of such altered recognition sites has delimited the sequences required for cleavage. The molecular genetics of mating-type interconversion is discussed in the context of this endonucleolytic activity. The second endonuclease, which we refer to as Sce II, is present in all strains of S. cerevisiae we have examined. The cleavage site of Sce II has been determined and proves to be unrelated to the cleavage site of YZ endo. © 1983