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KlCYC1encodes for cytochrome cin the yeast Kluyveromyces lactisand is transcribed in two mRNAs with different 3′‐processing points. This is an uncommon transcription mechanism in yeast mRNAs. The 3′ sequence encompassing the whole region that is needed to produce both mRNAs is analysed. We have determined identical processing points in K.lactisand in Saccharomyces cerevisiaecells transformed with KlCYC1; positions 698 and 1092 (with respect to the TAA) are the major polyadenylation points. This shows that the cis‐elements present in the KlCYC13′‐untranslated region (3′‐UTR) direct a processing mechanism that has been conserved in yeast. In K. lactisthere is a high predominance of the shorter transcript (1.14 kb) only at the initial logarithmic growth phase. Interestingly, this growth phase‐dependent regulation of 3′‐UTR processing is lost when the gene is expressed in S. cerevisiae. Copyright © 2001 John Wiley & Sons, Ltd.

The KlHEM1gene from Kluyveromyces lactisencodes a functional 5‐aminolevulinate synthase (δALA synthase), as confirmed by complementation of a hem1mutant Saccharomyces cerevisiaestrain, homology search, and detection of a 2·3 kb transcript. The gene is highly homologous to the ScHEM1gene, and the sequence of the promoter region contains a complex combination of putative regulatory signals. Some of them are related to phospholipid biosynthesis, glycolytic metabolism, and regulation by carbon source. Transcription of KlHEM1increased significantly in response to limited oxygen, and only slightly with the change from repressed (glucose) to derepressed conditions (glycerol). The δALA synthase from K. lactiscontains, in the amino‐terminal region, two heme‐responsive elements that are not present in the protein from Saccharomyces cerevisiae. The complete nucleotide sequence has been entered in the EMBL data library under Accession Number X92944. © 1997 John Wiley & Sons, Ltd.