Biochemical characterization of Sƒ9 Sp-family-like protein factors reveals interesting features

Abstract

We earlier documented the involvement of novel Sp-family-like protein factors in transcription from the Autographa californica nucleopolyhedrovirus (AcNPV) polyhedrin (polh) gene promoter [Ramachandran et al. (2001) J. Biol. Chem. 276: 23440-23449]. These zinc-dependent Sp-like factors bind to two putative Sp-factor-binding motifs, present within the AcSp sequence upstream of the polh promoter, with very high affinity (K_d = 2.1 × 10^-12M). Like other polh-promoter-associated host transcription factors, these Sp-like factors display tolerance to high ion concentrations up to even 3M NaCl. An electrophoretic mobility shift assay demonstrated a probable cross-talk between the Spodoptera frugiperda (Sƒ9) Sp-family-like proteins and the TFIID complex. In complementary experiments, specific replacements of the Sp-factor-binding motifs with TATA-like elements resulted in expression of a luciferase reporter gene to almost the same level as that obtained with a wild-type native construct. Our results point to the possibility of the involvement of TFIID and Sƒ9 Sp protein interaction in transcription from the baculovirus polyhedrin promoter.