Saccharomyces cerevisiae contains at least four PRS genes, all of which have been cloned and sequenced. Each of the four derived amino acid sequences have more than 60% similarity to the corresponding polypeptides of man, rat, Escherichia coli and Salmonella typhimurium. The PRS1 gene maps on chromosome XI, PRS2 on chromosome V, PRS3 on chromosome VIII and PRS4 on chromosome II. One member of this gene family, PRS1, contains a region of non-homology (NHR) shown by cDNA cloning and sequencing not to be an intron. The results presented here suggest that the presence of this NHR is not detrimental to the function of the gene. To date the possibility of protein splicing can be neither proven nor disputed.

We used quantitative real-time PCR analysis to measure the copy number of the BARE-1 retrotransposon in 5 cultivars of barley (Hordeum vulgare), as well as in samples from its wild relative, Hordeum spontaneum. Two sets of PCR primers were used to amplify regions within the long terminal repeat (LTR) and the reverse transcriptase (RT) gene of BARE-1 (GenBank accession Z17327). The LTR primers detected an average of 2.148 x 105 +/- 0.012 x 105 copies per haploid genome among barley samples, whereas the RT primers detected an average of 1.588 x 104 +/- 0.085 x 104 copies. The average ratio of LTR:RT was estimated to be 13.5:1. This finding indicates that more than 7% of the barley genome is occupied by BARE-1 elements in the form of solo LTRs and another 2.6% of the genome is occupied by the full-length element. Taken together, BARE-1 sequences represent approximately 9.6% of the barley genome among the barley plants used in this study. For the above estimation, a genome size of 5.44 x 103 Mb for H. vulgare and 5.39 x 103 Mb for H. spontaneum were assumed. Our study on quantification results of the BARE-1 for a small group of barley cultivars showed that there are significant differences among cultivars in terms of BARE-1 copy number, providing further evidence that BARE-1 is active and has a major role in shaping the barley genome as a result of breeding and selection. Quantification results also showed that most of the elements (> 90%) are present as truncated copies (solo LTRs). These results show that there is a high level of recombination leading to the formation of truncated elements and a subsequent DNA loss from the genome. Taken together, our study provides a glimpse into a dynamic micro-evolutionary process that is the by-product of genome reshuffling and directional selection in barley breeding programs.

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We have cloned and sequenced a Saccharomyces cerevisiae gene coding for a protein with significant similarities to the mitochondrial carrier family. The gene we termed YMC1 (yeast mitochondrial carrier) is located on chromosome XVI, closely downstream of ARO7 encoding chorismate mutase.

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