White Light Effects on the mRNA for the Light-Harvesting Chlorophyll a/b-Protein in Lemna gibba L. G-3

Translation products of poly(A) mRNA isolated from Lemna gibba L. G-3 include a major polypeptide of 32,000 daltons which is immunoprecipitated by antiserum to chlorophyll a/b-protein from Chlamydomonas. This 32,000 dalton polypeptide represents a precursor to the light-harvesting chlorophyll a/b-protein of molecular weight 28,000 found in the thylakoid membranes of Lemna gibba. The amount of this translatable mRNA decreases relative to other translatable mRNAs when green plants grown in continuous white light are placed in darkness. This decrease occurs rapidly. The most rapid decline occurs during the first day; after 4 days of darkness, only a low level of this mRNA can be detected by in vitro translation. When the plants are returned to white light there is an increase in the relative level of this mRNA which can be easily detected within two hours. The in vivo synthesis of this protein has been assayed under the different light conditions. The light effects on the in vivo synthesis of the chlorophyll a/b-protein reflect the light effects on the translatable mRNA for the polypeptide. The results indicate that light induced changes in the synthesis, processing, or degradation of chlorophyll a/b-protein mRNA could account for the light-induced changes observed in the effective synthesis rates for the chlorophyll a/b-protein in vivo.     

Control of synthesis of functional mRNA coding for phenylalanine ammonia-lyase from Rhodosporidium toruloides

The regulation of functional mRNA coding for phenylalanine ammonia-lyase (PAL) from Rhodosporidium toruloides was investigated. Polyadenylic acid [poly(A)]-containing RNA was an efficient template for in vitro translation in rabbit reticulocyte lysate. Non-poly(A)-containing RNA did not stimulate in vitro protein synthesis. Several lines of experimental evidence indicate that mRNA from R. toruloides directs PAL synthesis in reticulocyte lysate: (i) the major radioactive product in immunoprecipitates when lysates, incubated with yeast poly(A)-containing RNA, were reacted with PAL-antiserum had the same molecular weight as native PAL (75,000); (ii) this major radioactive product competes with authentic PAL for binding to PAL-antiserum; and (iii) partial proteolytic peptide maps of the in vitro translation product were very similar to those of native PAL. The levels of functional mRNA coding for PAL, when R. toruloides was grown in different physiological conditions, were determined by quantitation of PAL synthesized in vitro when RNA was added to reticulocyte lysate. Functional PAL mRNA was six times higher in yeast grown on phenylalanine compared with glucose-phenylalanine minimal medium. No functional PAL mRNA was detected in yeast grown on glucose-ammonia minimal medium in the presence or absence of phenylalanine. These observed changes in functional PAL mRNA were similar to levels of PAL catalytic and antigenic activity. The kinetics of functional PAL mRNA synthesis and degradation were studied. Maximum levels of functional PAL mRNA were observed within 60 min of transfer to PAL-inducing growth conditions. Poly(A)-containing RNA and functional PAL mRNA were rapidly degraded when cells were transferred from phenylalanine to glucose-ammonia minimal medium, with half-lives of 25 and 10 min, respectively. Thus, it is suggested that the alterations in the amount of PAL in cells of R. toruloides grown in different physiological conditions primarily result from alteration in the amount of functional mRNA coding for the enzyme.