Yeast CAL1 is a structural and functional homologue to the DPR1 (RAM) gene involved in ras processing

Abstract

A 2.3-kilobase pair DNA fragment of the yeast CAL1 gene was cloned by complementation of the cal1-1 mutation, which causes a defect in nuclear division and bud formation (Ohya, Y., Ohsumi, Y., and Anraku, Y. (1984) Mol. & Gen. Genet. 193, 389-394). Nucleotide sequencing of this fragment revealed a single open reading frame (ORF) encoding a polypeptide of 376 amino acids. Comparative analysis of the predicted amino acid sequence has shown that the CAL1 product has similarity to two yeast proteins: the DPR1 (RAM) gene product that is involved in processing of ras protein at the farnesylation step, and the essential ORF2 protein whose structural gene has a head-to-head arrangement with PRP4, which is involved in mRNA processing. Functional homology between CAL1 and DPR1 has also been suggested from genetic evidence that multiple copies of the CAL1 gene suppress the growth defects of a dpr1 null mutant at high temperature. This suppression is Ca(2+)-dependent, since it was not observed in complete medium containing 200 microM CaCl2 but was apparent in medium containing 100 mM CaCl2. From sequence analysis of the cal1-1 mutation, together with the alignment of the three gene products, we have concluded that the conserved Gly328 in the C terminus is important for activity. We suggest that the CAL1 protein participates in a ras-like C-terminal modification of proteins involved in nuclear division and bud growth.