Screening of the complete genome sequence from the yeast Saccharomyces cerevisiae reveals that 28 open reading frames (ORFs) are homologous to each other and to established bacterial members of the drug‐resistant subfamily of the major facilitator superfamily. The phylogenesis of these protein sequences shows that they fall into three major clusters. Cluster I contains 12 ORFs, cluster II contains ten ORFs and cluster III contains six ORFs. Hydropathy analyses indicate that in clusters II and III ORFs, 14 transmembrane spans are predicted whereas only 12 transmembrane spans are predicted in cluster I ORFs. Three ORFs that have known functions as multidrug‐resistance pumps in other yeast species such as Schizosaccharomyces pombe (CAR1), Candida albicans (BMRP) or C. maltosa (CYHR), also fall into cluster I. Two S. cerevisiae ORFs of known multidrug‐resistance function (ATR1, SGE1) fall into cluster II. Cluster III consists exclusively of ORFs of unknown function but binary sequence comparisons show homology to ORFs from cluster II. Analysis of the multiple alignment for these proteins leads to the identification of characteristic signature sequences for each of the three clusters. © 1997 by John Wiley & Sons, Ltd.

From the approximately 5000 open reading frames presently identified by systematic sequencing of the yeast genome, 100 Saccharomyces cerevisiae transport proteins belonging to the major facilitator superfamily (MFS), were assigned to 17 families on the basis of extensive database searches and binary comparisons. These families include multidrug resistance proteins and transport proteins for sugars, amino acids, uracil/ aliantoin, allantoate, phosphate, purine/cytosine, proteins, peptides, potassium, sulfate, and urea. Four new families of unknown function have been identified. For the sugar and amino acid transport proteins, alignments were made and phylogenetic trees were constructed allowing the identification of several clusters of proteins presumably exhibiting similar transport functions.

A cDNA clone was isolated for a fourth pma gene encoding a putative plasma membrane H(+)-ATPase of Nicotiana plumbaginifolia. The sequence of the predicted 952 residue PMA4 polypeptide was compared with those of other known plant PMAs, revealing a higher identity with the Arabidopsis thaliana proteins (86-89%) than with the other three N. plumbaginifolia PMA proteins (80-82%). This supports the view that there are two pma subfamilies which probably arose from a gene duplication predating the separation of the Dilleniidae and Asteridae plant subclasses. Measured pma4 transcript levels indicate that pma4 is similarly expressed in root, stem, leaf, and flower tissues, contrary to the pmal-3 subfamily whose members displayed differential expression according to the organ.

No abstract

No abstract