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 cerevislae. 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 degrees 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 TIR1 (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 hydrophobic 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.