High mobility group proteins 1 and 2 function as general class II transcription factors

Abstract

High mobility group (HMG) proteins 1 and 2 are thought to be associated with chromatin enriched in active gene sequences, to stimulate endogenous transcription of class II and III genes using HMG-depleted nuclei, and to bind specific DNA sequences upstream of the coding regions of trout HMG-T and human beta-globin genes. In testing the possibility that these proteins may act as general transcription factors, the run-off transcription of trout protamine, human beta-globin, adenovirus 2 major late promoter, and herpes simplex virus (HSV) thymidine kinase genes was found to be inhibited by affinity-purified HMG-1 and -2 antibodies. The inhibition was partially relieved by exogenously added HMG-1 or -2. A complementation assay showed that the 0.15 M KCl flowthrough of HeLa nuclear extract fractionated by anion-exchange chromatography (DE-52) could be replaced by purified HMG-1 and/or -2 to complement transcription of the trout protamine gene by the 0.5 M KCl eluate fraction. Inhibition studies with heparin showed that HMG-1 and -2 were required for initiation of transcription. These results indicate an absolute requirement of HMG-1 and -2 for class II gene transcription. Western blotting and transcription reconstituted with purified factors show a copurification of HMG-1 and -2 with factor II B, described earlier by Reinberg and Roeder [(1987) J. Biol. Chem. 262, 3310-3321].

The nonspecific DNA-binding and -bending proteins HMG1 and HMG2 promote the assembly of complex nucleoprotein structures.

“…They bind doubleand single-stranded DNA with no apparent sequence specificity, although they bind with markedly higher affinity to cruciform structures (Wright and Dixon 1988;Bianchi et al 1989) and cis-platin-modified DNA (Pil and Lippard 1992). The exact functions of HMG1 and HMG2 are not yet known, although stimulatory effects of HMG1 and HMG2 on transcription (Stoute and Marzluff 1982;Tremethick andMolloy 1986,1988;Singh and Dixon 1990), DNA replication (Alexandrova et al 1984;Alexandrova and Behchev 1988), and nucleosome assembly (Bonne-Andrea et al 1984) have been reported. Our results with the Hin site-specific recombination reaction suggest that one specific function of HMG1 and HMG2 is to promote assembly of higher order nucleoprotein complexes, a feature that may be common to each of the processes cited above.…”

Mutational and functional analysis of dominant SPT2 (SIN1) suppressor alleles in Saccharomyces cerevisiae.

“…These HMG proteins constitute an important class of nonhistone chromosomal proteins of eukaryotes (reviewed in references 35 and 77). Although their cellular function remains unknown, they have been implicated in nuclear processes such as transcription (71,76), DNA replication (32), and chromatin assembly (9). Consistent with a role in chromatin structure, it was shown that the SPT2/SIN1 protein is concentrated in the nucleus and that an increase in chromosome instability is observed in sinl mutants (42).…”

High mobility group protein, hmg‐1, contains insignificant glycosyl modification

“…) and plays a role in nucleosome assembly/disassembly (Bonne-Andrea et al, 1984;Waga et al, 1989), the regulation of transcription (Watt & Molloy, 1988;Singh & Dixon, 1990), binding to cruciform structures of DNA (Bianchi et al, 1989) and in chromatin (Scovell et al, 1987), and in the process of differentiation (Seyedin et al, 1981). There is a keen interest in gaining a greater understanding into the mechanism by which HMG-1 takes part or regulates these important activities.…”