Differential expression of the two distinct replication protein A subunits from Cryptosporidium parvum.

Apicomplexan parasites differ from their host by possessing at least two distinct types (long and short) of replication protein A large subunits (RPA1). Different roles for the long and short types of RPA1 proteins have been implied in early biochemical studies, but certain details remained to be elucidated. In the present study, we have found that the Cryptosporidium parvum short-type RPA1 (CpRPA1A) was highly expressed at S-phase in parasites during the early stage of merogony (a cell multiplication process unique to this group of parasites), but otherwise present in the cytosol at a much lower level in other cell-cycle stages. This observation indicates that CpRPA1A is probably responsible for the general DNA replication of the parasite. On the other hand, the long-type CpRPA1B protein was present in a much lower level in the early life cycle stages, but elevated at later stages involved in sexual development, indicating that CpRPA1B may play a role in DNA recombination. Additionally, CpRPA1B could be up-regulated by UV exposure, indicating that this long-type RPA1 is probably involved in DNA repair. Collectively, our data implies that the two RPA1 proteins in C. parvum are performing different roles during DNA replication, repair and recombination in this parasite.