Cold‐shock induction of a family of TIP1‐related proteins associated with the membrane in Saccharomyces cerevisiae

TIP1 is the first known cold‐shock‐and heat‐shock‐induced gene in Saccharomyces cerevisiae. Here it is demonstrated that a TIP1 homologue, TIR1, which had been previously cloned as SRP1 (serine‐rich protein), is strongly induced by a downshift in growth temperature from 30 to 10°C. We further cloned TIR2, which is transcribed at a low basal level but is increased strongly by cold shock and, to a lesser extent, by heat shock. The predicted protein sequence of TIR2 demonstrates remarkable homology to T1R1 (72.2%) and is also homologous with TIP1 (49%). TIP1, TIR1 and TIR2 are rich in both serine and alanine residues and each contains serine‐rich tandem repeats. The proteins contain putative N‐terminal signal peptides as well as hydro‐phobic C‐terminal sequences, indicating that the proteins may be membrane bound. The predicted protein sequences are also consistent with extensive O‐mannosylation as well as glycosyl‐phosphatidyl inositol (GPI) membrane anchoring. Cell fractionation analysis as well as studies using a yeast strain that is conditionally deficient in glycosylation demonstrate that TIP1 is a heavily modified membrane‐associated protein. Single, double combinations and triple mutants were created and none demonstrated any obvious phenotype, indicating that this family of genes is not essential for normal growth.