A novel multifunctional factor involved in trans-splicing of chloroplast introns in Chlamydomonas.
In the chloroplast of Chlamydomonas reinhardtii, psaA mRNA is spliced in trans from three separate precursors which assemble to form two group II introns. A fourth transcript, tscA, completes the structure of the first intron. Of the fourteen nucleus-encoded factors involved in psaA splicing, only two are required for splicing of both introns. We cloned and characterized the first of these more general factors, Raa1. Consistently with its role in psaA splicing, Raa1 is imported in the chloroplast where it is found in a membrane fraction and is part of a large ribonucleoprotein complex. One mutant, raa1-L137H, is defective for splicing of both introns, but another allelic mutant, raa1-314B, still expresses the 3' part of the Raa1 gene and is deficient only in splicing of intron 2. This observation and a deletion analysis indicate the presence of two domains in Raa1. The C-terminal domain is necessary and sufficient for processing of tscA RNA and splicing of the first intron, while the central domain is essential for splicing of the second intron. The combination of these two functional domains in Raa1 suggests that this new factor may coordinate trans-splicing of the two introns to improve the efficiency of psaA maturation.
Merendino
Livia
L
Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, CH-1211 Geneva 4, Switzerland.
Perron
Karl
K
Rahire
Michèle
M
Howald
Isabelle
I
Rochaix
Jean-David
JD
Goldschmidt-Clermont
Michel
M
D020418:Algal Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism; D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D007438:Introns; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D020449:Repetitive Sequences, Amino Acid; D012260:Ribonucleases / Q000378:metabolism; D020040:Trans-Splicing
D020418:Algal Proteins; D008565:Membrane Proteins; D015800:Protozoan Proteins; D016601:RNA-Binding Proteins; C093455:tscA protein, Chlamydomonas; D012260:Ribonucleases