title: Sensing and responding to UV-A in cyanobacteria.
abstract: Ultraviolet (UV) radiation can cause stresses or act as a photoregulatory signal depending on its wavelengths and fluence rates. Although the most harmful effects of UV on living cells are generally attributed to UV-B radiation, UV-A radiation can also affect many aspects of cellular processes. In cyanobacteria, most studies have concentrated on the damaging effect of UV and defense mechanisms to withstand UV stress. However, little is known about the activation mechanism of signaling components or their pathways which are implicated in the process following UV irradiation. Motile cyanobacteria use a very precise negative phototaxis signaling system to move away from high levels of solar radiation, which is an effective escape mechanism to avoid the detrimental effects of  UV radiation. Recently, two different UV-A-induced signaling systems for regulating cyanobacterial phototaxis were characterized at the photophysiological and molecular levels. Here, we review the current understanding of the UV-A mediated signaling pathways in the context of the UV-A perception mechanism, early signaling components, and negative phototactic responses. In addition, increasing evidences supporting a role of pterins in response to UV radiation are discussed. We outline the effect of UV-induced cell damage, associated signaling molecules, and programmed cell death under UV-mediated oxidative stress.
authors.affiliation: Division of Life Science, Korea Basic Science Institute, Daejeon 305-806, Korea. chungyh@kbsi.re.kr.
authors.forename: Yoon-Jung
authors.initials: YJ
authors.lastname: Moon
authors.forename: Seung Il
authors.initials: SI
authors.lastname: Kim
authors.forename: Young-Ho
authors.initials: YH
authors.lastname: Chung
mesh_terms: D056931:Cryptochromes / Q000502:physiology; D000458:Cyanobacteria / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects*; D055537:Light Signal Transduction; D018384:Oxidative Stress / Q000528:radiation effects; D011622:Pterins / Q000378:metabolism / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D056931:Cryptochromes; D011622:Pterins; D017382:Reactive Oxygen Species