Ultraviolet mutagenesis and inducible DNA repair in Caulobacter crescentus

The ability to reactivate ultraviolet (UV) damaged phage ΦCbK (W-reactivation) is induced by UV irradiation of Caulobacter crescentus cells. Induction of W-reactivation potential is specific for phage ΦCbK, requires protein synthesis, and is greatly reduced in the presence of the rec-526 mutation. The induction signal generated by UV irradiation is transient, lasting about 1 1/2–2 h at 30°C; if chloramphenicol is present during early times after UV irradiation, induction of W-reactivation does not occur. Induction is maximal when cells are exposed to 5–10 J/m 2 of UV, a dose that also results in considerable mutagenesis of the cells. Taken together, these observations demonstrate the existence of a UV inducible, protein synthesis requiring, transiently signalled, rec -requiring DNA repair system analogous to W-reactivation in Escherichia coli . In addition, C. crescentus also has an efficient photoreactivation system that reverses UV damage in the presence of strong visible light.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47557/1/438_2004_Article_BF00329935.pd

Nucleosome architecture throughout the cell cycle

Nucleosomes provide additional regulatory mechanisms to transcription and DNA replication by mediating the access of proteins to DNA. During the cell cycle chromatin undergoes several conformational changes, however the functional significance of these changes to cellular processes are largely unexplored. Here, we present the first comprehensive genome-wide study of nucleosome plasticity at single base-pair resolution along the cell cycle in Saccharomyces cerevisiae. We determined nucleosome organization with a specific focus on two regulatory regions: transcription start sites (TSSs) and replication origins (ORIs). During the cell cycle, nucleosomes around TSSs display rearrangements in a cyclic manner. In contrast to gap (G1 and G2) phases, nucleosomes have a fuzzier organization during S and M phases, Moreover, the choreography of nucleosome rearrangements correlate with changes in gene expression during the cell cycle, indicating a strong association between nucleosomes and cell cycle-dependent gene functionality. On the other hand, nucleosomes are more dynamic around ORIs along the cell cycle, albeit with tighter regulation in early firing origins, implying the functional role of nucleosomes on replication origins. Our study provides a dynamic picture of nucleosome organization throughout the cell cycle and highlights the subsequent impact on transcription and replication activity.This work was supported by the Spanish Ministry of Science and Innovation (BIO2012-32868), Instituto de Salud Carlos III (INB) and the European Research Council (SimDNA project)