Ier5, a novel member of the slow-kinetics immediate-early genes

We describe here a novel member of the slow-kinetics immediate-early gene f amily. Ier5 is an intronless gene, encoding a serum and growth factor-induc ible message of 2123 nucleotides that is present in a wide variety of tissu es. The predicted open reading frame encodes a 308-amino-acid, highly proli ne-rich protein with homology to the amino terminus of the immediate-early gene pip92/Ier2/ETR101. Ier5 is predicted to be a nuclear protein and conta ins a PEST-like sequence, suggesting rapid protein degradation. Multiple ph osphorylation sites are present. Ier5 shows growth factor induction kinetic s similar to that of pip92/Ier2/ETR101, but unlike pip92/Ier2/ETR101 does n ot appear to require phosphokinase C activity for transcriptional activatio n. The sequence of the promoter region of Ier5 was determined and examined for transcription factor binding sites thought to mediate serum and growth factor response. Multiple AP-1 sites and an Ets-1 site were observed, but t he CArG and CArG-like boxes of the serum response element were absent. The predicted nuclear localization of Ier5, coupled with the potential for rapi d regulation by phosphorylation and/or degradation, suggests that Ier5 may play an important role in mediating the cellular response to mitogenic sign als. (C) 1999 Academic Press.