Characterization of single-stranded DNA binding proteins in rat glial-enriched nuclei

Single-stranded DNA binding proteins (SSBs) are those proteins which preferentially bind single-stranded DNA as opposed to double-stranded DNA and are known to be involved in recombination, amplification, and repair of DNA. To characterize single-stranded DNA binding proteins of glial cells and to examine their potential involvement in induction of neurogenic tumors in rats, nuclei were isolated from target glia and non-target liver of carcinogenically sensitive Sprague-Dawley (SD) and resistant Berlin-Druckrey-IV (BD-IV) rats of various ages and rapidly proliferating glioma cells. Nuclei were fractionated into chromatin, a preribosomal RNA protein complex, heterogeneous nuclear ribonucleoprotein complex (hnRNP), and nucleoplasm. SSBs were isolated, quantitated, and characterized by electrophoresis. A comparison of the contents of SSBs relative to RNA and their electrophoretic profiles between chromatin and hnRNP revealed that SSBs of liver chromatin were mainly associated with RNA. However, it was found that glial chromatin, particularly that of juvenile rats, was enriched with a heterogeneous series of SSBs which were not found in liver chromatin and presumably associated with chromosomal DNA. Some of these SSBs were enriched in glial chromatin of sensitive SD rats compared with that of resistant BD-IV rats. High mobility group proteins (HMG) 1 and 2 constituted major SSB components in the nucleoplasm and a greater amount of these HMGs were found in juvenile glia, compared to adult glia and juvenile and adult liver. Fractionation of glial SSBs and determination of their biological functions may contribute to the further understanding of the role these proteins may play in the processes of carcinogenesis.