POF1 and PCT1 sequences and functional analyses. (A) Clustal W (Megalign software) primary sequence alignment of the cytidylyltransferase family. The conserved motif HxxH is enclosed in the box. Ct human = choline cytidylyltransferase from humans (gi 166214967); et human = ethanolamine cytidylyltransferase from humans (gi 1817548); pct1 yeast = phosphocholine cytidylyltransferase from S. cerevisiae (gi 1323361); ycl047c = Pof1p (gi 6319802). (B) Complementation assays. The cells were exposed to heat shock (37°C) or control conditions (30°C) for 17 h, serially diluted and spotted on YPD plates, which were incubated for 48 h at 30°C and photographed. The asterisk denotes cells transformed with the plasmid pYES-TOPO+POF1 for overexpression of Pof1.