NUCLEOTIDE-SEQUENCE AND EXPRESSION OF RIBOSOMAL-PROTEIN S3 MESSENGER-RNA DURING EMBRYOGENESIS IN THE MEXICAN AXOLOTL (AMBYSTOMA-MEXICANUM)

We have isolated and sequenced a full-length (0.9 kb) cDNA clone of ri bosomal protein S3 by subtraction hybridization using a single-strande d cDNA library from stage 25-27 (tracer) and the mRNA from stage 15-17 (driver) of embryonic Mexican axolotl (Ambystoma mexicanum). The axol otl is a unique animal model for studying heart development as well as myofibrillogenesis because it carries a mutation in gene (c) under ba r. The deduced amino acid sequence of axolotl S3 protein shows about 9 3.9% identity with human S3 protein over a 243 amino acid residue over lap. When compared with mouse and Xenopus laevis ribosomal S3 proteins , the axolotl sequence shows 94.3 and 93.9% identity respectively. Int erestingly, the axolotl S3 sequence shows higher identity at the nucle ic acid level with human and/or other mammals than with Xenopus. The S 3 transcript, as determined by RT-PCR, is present at stage 2-4 in a lo wer amount and the onset of transcription is most likely at the beginn ing of gastrulation (10-12). The expression level of S3 transcripts re aches a maximum by mid gastrulation (stages 13-14) and then follows a biphasic pattern being lower at stages 16-17 with subsequently steady increases until the mid tailbud stages (25-27).