Structures of monomeric, dimeric and trimeric PCNA: PCNA-ring assembly and opening.

DNA sliding clamps form an oligomeric ring encircling DNA and serve as a moving platform for DNA-processing proteins. The opening and closing of a sliding-clamp ring is essential to load the clamp onto DNA in order to perform its functions. The molecular details of how clamp rings open and enclose DNA are still not clear.

Purification, crystallization and preliminary X-ray analysis of two crystal forms of ribonuclease Sa3.

RNase Sa3 produced by Streptomyces aureofaciens strain CCM 3239 belongs to the T1 family of microbial ribonucleases. It is closely related both to RNase Sa, studied in detail earlier, and to RNase Sa2 produced by the same microorganism. The most important property of RNase Sa3 is the relatively high cytotoxic activity, which was not observed for RNase Sa and Sa2.