THE CENTROSOMAL PROTEIN CENTROSOMIN-A AND THE NUCLEAR-PROTEIN CENTROSOMIN-B DERIVE FROM ONE GENE BY POSTTRANSCRIPTIONAL PROCESSES INVOLVINGRNA EDITING

The identification of a gene encoding concomitantly a nuclear protein and an intrinsic centrosomal protein further emphasizes the close and presumably developmental relationship between the cell nucleus and the centrosome. Screening of a murine RNA-based cDNA library with an anti serum to a centrosomal protein and rescreening with the insert of an i nitial clone released two complete cDNAs (1.2 kbp and 2.2 kbp) coding for proteins with notable characteristics. The amino-terminal sections of centrosomin A (276 amino acid residues, molecular mass 34.5 kDa) a nd of centrosomin B (447 amino acid residues, molecular mass 54.8 kDa) are identical over 272 amino acid residues, The carboxy-terminal sect ion of the larger protein comprises additional 175 amino acid residues including nuclear location signals. The mRNAs encoding centrosomin A and B derive from a single gene. Chromosomal mapping (FISH) shows only one significantly hybridizing gene locus on chromosome 19D. PCR with genomic DNA as template and primer pairs complementary to the sequence which is identical in centrosomin A and B cDNAs results in amplificat ion of only one DNA fragment, Moreover, one exon of the genomic sequen ce and the centrosomin B-encoding cDNA sequence include a G which is d eleted in the centrosomin A-encoding cDNA, Accordingly, the two mRNAs are the products of either alternative splicing or alternative polyade nylation in combination with RNA editing, The recombinantly expressed chimeric protein consisting of centrosomin A and the green fluorescent protein from Aequorea victoria accumulates in centrosomes while the c orresponding fusion protein with the centrosomin B sequence is transpo rted into nuclei.