Studies on nonhistone chromosomal proteins

In the second part of this study, possible alteration of nonhistone chromosomal proteins during infection of NIH 3T3 cells with murine leukemia virus (MuLV) was investigated. Sucrose gradient analyses of viral DNAs reveal that MuLV DNA is in the form of a nucleoprotein complex, which was distinctly different from the minichromosome form found with the SV40 viral DNA. It was also found that circular forms of MuLV DNAs could be extracted from host chromatin with O.35 M NaCl. This is the same salt concentration that removes a large portion of nonhistone proteins from chromatin. This suggests the possibility of interaction between viral DNA and loosely bound nonhistone proteins. Also, various cellular protein fractions, including the nonhistone protein fractions, were isolated from NIH 3T3 cells which were uninfected, acutely infected, and chronically infected with MuLV. These proteins, which were ³[H] leucine labeled, were subjected to various electrophoretic analyses. Numerous differences in the protein complement isolated from the three groups of NIH 3T3 cells were observed. The major differences were present between the chronically infected cell group and the other two groups of cells.