Chloroplast ribosomal protein L-18 in Chlamydomonas reinhardtii is processed during ribosome assembly.
Chloroplast ribosomal protein L-18 is made in the cytoplasm as a precursor, imported into the chloroplast, and processed to the mature form in two steps. We report here that the intermediate produced following the first processing step associates specifically with a ribosomal complex migrating with the chloroplast ribosome large subunit peak in sucrose gradients, and is then processed into mature L-18. This processing event is slowed down in mutant cells deficient in synthesis of non-ribosomal proteins in the chloroplast. Thus the second processing step of L-18 occurs during ribosome assembly, depends on one or more nonribosomal proteins made in the chloroplast, and may be required for the maturation of the 50 S ribosome subunit. The mature L-18 protein shows extensive sequence homology at its amino-terminus to Escherichia coli ribosomal protein L27, which is located at the interface between 30 S and 50 S subunits and is involved in the formation of the peptidyl-tRNA binding site.
Liu
X Q
XQ
Department of Botany, Duke University, Durham, NC 27706.
Gillham
N W
NW
Boynton
J E
JE
D000595:Amino Acid Sequence; D002696:Chlamydomonas / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D004926:Escherichia coli / Q000032:analysis; D008969:Molecular Sequence Data; D010779:Photofluorography; D011499:Protein Processing, Post-Translational; D012269:Ribosomal Proteins / Q000378:metabolism*; D012270:Ribosomes
D012269:Ribosomal Proteins; C029609:ribosomal protein L18; C034661:ribosomal proteins L27