A Cytoplasmic Regulatory Mutant of Euglena: Constitutivity for the Light-Inducible Chloroplast Transfer RNAs

Abstract

An ultraviolet-induced cytoplasmic mutant (GIBU) In Euglena, the chloroplastic species of tRNA and of aminoacyl-tRNA synthetases appear to be quantitatively regulated by light; i.e., exposure of dark-grown wild-type cells to light results in a striking increase in the quantity of these organelle translational macromolecules (1-3). The present report represents an initial attempt to elucidate the control mechanism(s) involved in the light induction of chloroplast tRNAs, through the use of chloroplhstic mutants (4-6) ofEuglena. In these studies we examined mutants of Euglena gracilis Klebs var. bacillaris Pringsheim for the loss of normal control of chloroplast tRNA biosynthesis. In particular, we describe one mutant (GIBU), which was induced by ultraviolet irradiation, but appears to be a regulatory "constitutive" mutant in the sense that, in contrast to wild type, certain chloroplast tRNAs are present in repressed (or darkgrown) mutant cells at approximately the same level as that found in induced (or light-grown) cells.MATERIALS AND METHODS tRNA Was Prepared from Euglena cells in the logarithmic growth phase as described (3).tRNA Chromatography. The reversed-phase system described by Weiss and Kelmers (7) was used -with columns 225 X 1.5 cm. For chromatographic comparisons, approximately equal amounts (in cpm) of 14C-and 3H-labeled aminoacyl-tRNAs were applied to the columns. The chromatography is described in the legend to tRNAs from cells grown in the light and the dark were acylated with a synthetase preparation (1) from cells grown in the light and chromatographed as described in (A) except that the NaCl gradient was from 0.40-0.55 M. 1749I To whom reprint requests should be addressed.

Changes in the expression of the chloroplast genome of Euglena gracilis during chloroplast development

“…The Euglena chloroplast DNA exists as a covalently closed, circular duplex molecule of molecular weight 92 X I06 (Manning and Richards, 1972). The chloroplast chromosome codes for chloroplast rRNA (Scott and Smillie, 1967; Stutz and Rawson, 1970), and possibly chloroplast transfer RNA (Goins et al, 1973). Although Euglena chloroplast coded proteins have not been described, the genome in principle could also code for 200-300 proteins of molecular weight 40000.…”

Photo and Nutritional Regulation of Euglena Organelle Development

“…Proplastids in dark grown cells have low levels of chloroplast rRNA (Chelm et al 1977b(Chelm et al , 1978(Chelm et al , 1979Cohen and Schiff 1976;Geimer et al 2009;Rawson et al 1981) and tRNA (Goins et al 1973;Reger et al 1970;Schwartzbach et al 1976a). The cellular content of chloroplast rRNA and chloroplast tRNA increases from approximately 5-25% of the cellular rRNA and tRNA content after 72 h of light exposure (Chelm et al 1977b(Chelm et al , 1978(Chelm et al , 1979Cohen and Schiff 1976;Rawson et al 1981;Schwartzbach et al 1976a).…”

“…Chloroplast encoded proteins are synthesized within the chloroplast using chloroplast ribosomes (Schwartzbach et al 1974) tRNAs, (Goins et al 1973;Hallick et al 1984;Reger et al 1970;Schwartzbach et al 1976a) and tRNA synthetases (Barnett et al 1976;Hecker et al 1974;Parthier et al 1972;Reger et al 1970). Proplastids in dark grown cells have low levels of chloroplast rRNA (Chelm et al 1977b(Chelm et al , 1978(Chelm et al , 1979Cohen and Schiff 1976;Geimer et al 2009;Rawson et al 1981) and tRNA (Goins et al 1973;Reger et al 1970;Schwartzbach et al 1976a).…”