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Six novel Open Reading Frames (ORFs) located on the left arm of chromosome XII (YLL044w, YLL042c, YLL040c, YLL038c, YLL035w and YLL034c) have been analysed using short-¯anking homology (SFH) gene replacement. Sporulation and tetrad analysis showed that YLL035w and YLL034c are essential for cell growth; yll035w spores arrested after two or three cell divisions, while the majority of yll034c spores stopped growth within two cell cycles after germination. Complementation of the yll035w deletion with its cognate clone, and a promotersubstitution experiment, indicated that the promoter of YLL035w may lie within the adjacent ORF, YLL036c. Transcriptional analysis demonstrated that YLL035w is under cell-cycle regulation. Bioinformatic analyses produced signi®cant matches between YLL034c and mammalian valosin and many other ATPases. The standard EUROFAN growth tests failed to reveal obvious phenotypes resulting from deletion of any of the four nonessential ORFs. Replacement cassettes, comprising the kanMX marker¯anked by each ORF's promoter and terminator regions, were cloned into pUG7. All the cognate clones, except for YLL040c, were generated using direct PCR products ampli®ed from genomic DNA or using gap-repair. All clones and strains produced have been deposited in the EUROFAN genetic stock centre (EUROSCARF, Frankfurt).

Deletion, together with basic functional and bioinformatic analyses has been carried out on eight novel ORFs discovered during the sequencing of the Saccharomyces cerevisiae genome. Six ORFs (YLL049w, YLL051c, YLL052c, YLL053c, YLL054c and YLL055w) located on the left arm, and one (YLR130c) on the right arm, of chromosome XII, and an eighth ORF (YNL331c) on the left arm of the chromosome XIV, have been investigated. ORFs were deleted by the SFH–PCR gene‐replacement strategy. Basic functional analysis revealed no obvious phenotype for any of the eight ORFs. Bioinformatic analysis, however, revealed possible functions for seven of the ORFs on the basis of the amino acid sequence similarity of their predicted protein products to those of proteins with known functions. ORF YLL051c (FRE6) shows similarity to iron transport proteins, such as ferric reductase. YLL052c and YLL053c appear to be aquaporins. The product of YLL054c (Yll054p) is highly similar to the oleate‐specific transcriptional activator protein (Pip2p), which is involved in the peroxisomal induction pathway (pip). ORF YLL055w is similar to Dal5p, allantoate permease, and may play role in allantoin transport. YLR130c (ZRT2) is a low‐affinity zinc transporter protein. YNL331c is also named AAD14, which is induced by chemicals that induce oxidative stress by depleting the cell of glutathione. Copyright © 2000 John Wiley & Sons, Ltd.

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