Evidence for a Histone-Like Nucleoprotein in Chlamydia

摘要

Chlamydia has a biphasic life cycle alternating between the elementary body, specialized for extracellular survival, and the reticulate body, the replicative, intracellular form. The molecular genomic configuration of the elementary body and the reticulate body differ. Electron microscopy has shown loose arrangement of reticulate body DNA surrounded by a delicate membrane. Elementary bodies, however, have condensed DNA and rigid outer membranes. Attempts by Hackstadt et al. (1985) to initiate the differentiation of elementary bodies resulted in outer membrane changes; nevertheless, this did not result in elementary body to reticulate body transitions. Reduction of the outer membrane was insufficient to alter the condensed DNA structure. Thus, the growth cycle is probably dependent on changes in the genomic configuration of chlamydial DNA, as well as outer membrane changes. Intracellular, DNA binding proteins with histone-like properties have been isolated in a number of procaryotes including the thermophilic mycoplasma, Hemophilus influenzae, Bacillus sp.m and Escherichia coli, In E. coli, they consist of a least two basic polypeptide chains 19, of approximately 9,000 and 15-17,000 m.w. These nucleoproteins participate in DNA compaction equivalent to that seen in the nucleosome. They protect double-stranded DNA from micrococcal nuclease digestion., Also, they prevent thermal denaturation and enhance reannealing of single-stranded DNA.