The effect of irradiance and specific inhibitors on protein and nucleic acid synthesis in the marine cyanobacterium Synechococcus sp. WH 7803

Abstract

Direct measurements of protein and RNA synthesis have been made in the marine chroococcoid cyanobacterium Synechococcus sp. WH 7803 utilizing ³H-labelled leucine and uracil respectively. Both substrates were readily assimilated in the light, although leucine is incorporated much more rapidly and to a far greater extent than uracil. Exponentially dividing cells incorporated leucine into low and high molecular weight fractions at similar rates over a wide range of irradiances in short-term incubations. Incorporation into protein was greatly reduced in the dark. ³H-uracil assimilation was closely linked to the incubation irradiance, and incorporation into RNA was climinated in the dark. Addition of the photosynthetic inhibitor DCMU resulted in patterns similar to those found in the dark for both substrates. Additionally, specific inhibitors for transcription (rifampicin) and translation (chloramphenicol) eliminated incorporation of the substrates into the target fractions. The results indicate that these substrates provide a valid means to examine basic physiological characteristics in these important marine organisms.