Identification of novel components of the Ced and Ups systems in Saccharolobus islandicus REY15A

Abstract

In the cells of Sulfolobales, the Ced (Crenarchaeal system for exchange of DNA) and Ups (UV-inducible pili of Sulfolobus) systems are highly induced by DNA damages and function in chromosomal DNA exchange by mediating DNA import and cell aggregation, respectively. The Ced system is composed of CedA, CedA1, CedA2, and CedB. The Ups is composed of UpsA, UpsB, UpsE and UpsF. However, how the DNA is transported by these systems is far from clear. Here, we report two novel components of the Ced system, CedD (SiRe_1715) and CedE (SiRe_2100), which are paralogs of CedB and CedA, respectively, and one new component of the Ups system, UpsC (SiRe_1957), which is a paralog of UpsA and UpsB, in Saccharolobus islandicus REY15A. DNA exchange assay revealed that cedD, cedE, and upsC are essential for DNA import while cedE and upsC are also important for DNA export. Further microscopy analysis revealed that upsC is involved in cell aggregation like other Ups genes. Besides, we found that cedB and cedD co-occur in the genomes of crenarchaea which lack virB4 and the presence of cedB and cedD, and virB4 is complementary. Both proteins show homology to different parts of the N-terminal domain of VirB4 in a complementary manner and form stable homo-oligomers in vitro. Collectively, our results indicate that CedD and CedE, and UpsC are essential components of the Ced and Ups systems, respectively.