The proportion of sperm with DNA fragmentation appears to be potentially useful as a predictor of ICSI outcome, whereas embryo quality based on morphological criteria, appeared unaffected by DNA fragmentation.

DNA methylation level in human sperm could represent a new approach to study the ability of sperm to lead to pregnancy in an assisted reproduction procedure, especially when sperm samples with normal characteristics are used.

Pichia sorbitophila grows rapidly in the presence of very high NaCl concentrations. Under these conditions, even when the K + concentration is low, P. sorbitophila cells can maintain low Na + and high K + contents. This remarkable capacity of P. sorbitophila fails when the external pH is not acidic. This indicates that Na + efflux is mediated by an electroneutral Na + /H + antiporter. We have cloned and sequenced two genes designated as PsNHA1 and PsNHA2, which probably encode two antiporters of this type. The genes present high similarity with the corresponding genes from other yeasts. The heterologous expression of PsNHA1 or PsNHA2 in a Saccharomyces cerevisiae mutant lacking the Na + efflux systems and sensitive to high concentrations of Na + and K + rescued the tolerance and the ability to extrude both cations. The Accession Nos of the sequenced DNA fragments are: PsNHA1, AJ496431; PsNHA2, AJ496432. (TC 2.A.36)

The genomes of Zygosaccharomyces rouxii and Pichia sorbitophila were partially explored. The genome of Z. rouxii CBS 732 consists of seven chromosomes with an approximate size of 1.0-2.75 Mb, 12.8 Mb in total. Five of the chromosomes were labelled with specific probes. Three Z. rouxii genomic DNA fragments were sequenced; all 10 ORFs found were without introns and they have homologues in S. cerevisiae. Gene order comparison revealed that the organization is partially conserved in both species. The genome of P. sorbitophila CBS 7064 consists of seven chromosomes with an approximate size of 1.0-2.9 Mb, 13.9 Mb in total. Three of the chromosomes were labelled with specific probes. The sequencing of a 5.2 kb genomic DNA fragment revealed three ORFs, but no conservation of their organization was found, although all of them have their respective homologues in S. cerevisiae. According to our results, the presence of two overlapping ORFs in S. cerevisiae (YJL107c-YJL108c) could be interpreted as the result of a frameshift mutation.