Distribution patterns of three subfractions of drosophila nonhistone chromosomal proteins: possible correlations with gene activity.

The distribution of three molecular weight subfractions of the Drosophila nonhistone chromosomal proteins (NHC proteins) has been studied using an immunofluorescent technique (Silver and Elgin, 1976). In all three cases, the fluorescence distribution patterns obtained are distinct and reproducible. The results imply that different NHC protein components have different distributions along the polytene chromosomes. A highly selective pattern is obtained using antiserum against subfraction ?; puffs (loci highly active in RNA synthesis) and many nonpuffed chromomeres which are known to puff at other times during the third larval instar or prepupal stages are brightly fluorescent. New RNA synthesis can be induced at 87A, 87B-C1 and other chromomeres by heat shock treatment; these loci, previously stained at low levels, are subsequently stained brightly using the ? serum. The staining of the heat shock puffs appears to be superimposed upon the prior ? pattern. The results suggest that a change in chromosomal structure, as indicated by staining using the ? serum, is associated with gene activity as indicated by puffing. This different chromosomal structure may be the consequence of either a redistribution of a ? antigenic determinant a new association of specific protein(s) with the active sites] or a change in chromatin configuration making the ? antigenic determinant(s) newly available to the antibody probe].