Baculovirus‐expressed myogenic determination factors require E12 complex formation for binding to the myosin‐light‐chain enhancer

Two recombinant baculoviruses BcV‐myf4 and BcV‐myf5 have been constructed to synthesize the human myogenic determination factors myogenin (myf4) and myf5 in eucaryotic cells. Both recombinant proteins are localized to the nucleus of virus‐infected Spodoroptera frugiperda (sf) insect cells and can be recovered as soluble factors. The virus‐produced proteins exhibit high‐affinity binding to a muscle‐specific DNA sequence in the presence of the ubiquitous helix‐loop‐helix (HLH) protein E12, but only marginal binding in unsupplemented sf nuclear extracts. Both baculovirus‐encoded myogenic factors are able to heterooligomerize with E12 in the absence of DNA‐binding sites. We conclude from our results that these muscle‐specific HLH proteins produced in eucaryotic cells largely depend on dimerization with E12 or similar HLH proteins to recognize the myosin‐light‐chain‐enhancer‐MEF‐1‐binding site. We have no evidence for intracellular protein modifications exerting major effects on the interaction between these factors and DNA.