Abstract

• CAAT-binding transcription factor(CTF) proteins are implicated in the expression of multipleforms and are probably identical to nuclear facfor-1(NF-1). In herpes simplex virus thymidinekinase gene, CTF is required not only to induce basal transcription of this gene, but also tostimlulate the transcription of this gene by thyroid hormone. Gel mobility shift assays and biotin-avidin protein-DNA binding assays were performed to investigate if the synthesis of transcription factors which bind to CCAAT sequences of the TK promoter(CTF or CTF-like factors) is stimulated by T₃ and to kdentify the CCAAT-binding proteins in GH₄C₁ cells havingendogenous thyroid hormone receptors. There are two different sized(31 and 33 kDa) CCAAT-binding proteins in GH₄C₁ cells having endogenous thyroid hormone receptors. The synthesisof these CTF-binding proteins were not affected by T₃.