High mobility group proteins 1 and 2 are present in simian virus 40 provirions, but not in virions

Viral particles at the late stages of SV40 morphogenesis were examined for the presence of HMG proteins 1 and 2, by an immunochemical method involving the transfer of proteins from polyacrylamide gels to nitrocellulose membranes. It was found that these proteins are present in SV40 provirions, in which histone H1 is still associated with viral chromatin, but absent in mature SV40 virions.