High mobility group proteins 1 and 2 stimulate binding of a specific transcription factor to the adenovirus major late promoter.

High mobility group proteins 1 and 2 (HMGs 1 and 2) are abundant chromosomal proteins which are believed to be preferentially associated with regions of active chromatin. Our previous results have shown that HMGs 1 and 2 can significantly stimulate specific transcription in vitro from the adenovirus major late promoter. This stimulation is now shown to be due, at least in part, to the influence of HMGs 1 and 2 on binding of a specific transcription factor (MLTF) upstream of the start site of the gene to a region (-66 to -51) which is required for optimal transcription both in vivo and in vitro. HMGs 1 and 2 cause both an increase in the rate of binding of the transcription factor to the DNA and alterations to the pattern of the DNaseI footprint of the factor on the DNA. Different binding states of the factor are also observed dependent on the presence of MgCl2, the factor being bound but not protecting the binding region from DNaseI in the absence of MgCl2.