PHYSICAL MAPPING AND STRUCTURAL-ANALYSIS OF NEW GENE FAMILIES RT1.S AND RPS2R IN THE GRC REGION OF THE RAT MAJOR HISTOCOMPATIBILITY COMPLEX

Five new genes were identified in the growth and reproduction complex (grc) region: RT1.S1, RT1.S2, Rps2r1, Rps2r2, and Rps2r3. The class Ib RT1.S1 and RT1.S2 genes have five distinct exons (1, 4, 5, 6, 7) simi lar to other class I major histocompatibility complex genes but the co nventional exons 2 and 3 are absent. The genes are 97% similar, have C AAT and TATA boxes much upstream of the conventional position, obey th e GT/AG rule in their exon-intron boundaries, and are transcribed at a low level in thymus and testis but not in the liver and spleen. The r egion between exon 1 and exon 4 was analyzed by obtaining transcripts by reverse transcription-polymerase chain reaction (RT-PCR) amplificat ion which revealed the presence of four alternatively spliced mRNA tra nscripts of RT1.S1: 1) S1-1 (clones 14 and 16) has no exon between exo ns 1 and 4; 2) S1-2 (clones 7 and 8) has an exon of 45 nucleotides tha t can translate into 15 amino acids; 3) S1-3 (clone 5) has an exon of 42 nucleotides with a stop codon; and 4) S1-4 (clone 10) has two exons of 42 and 38 nucleotides, respectively, with stop codons. Only one RT 1.S2 mRNA transcript was obtained, and it has an exon of 45 nucleotide s between exon 1 and exon 4 which can form a peptide identical to the S1-2 isoform for that region. The 45 nucleotide exon between exon 1 an d exon 4 was unique for RT1.S2 and RT1.S2 and only matched a sequence in the RT1.0 intron region (nucleotides 2905-2949). The three ribosoma l-protein-S2-related (Rps2r) genes are 94%-98% similar; they are relat ed to the genes encoding ribosomal protein S2 of the black rat and the LLRep3 genes of the mouse and the human and to the genes encoding Sac charomyces cerevisiae S4, Escherichia coli S5, and other members of pr okaryote S5 family. The Rps2r1 gene is located just outside of the grc region. The Rps2r2 and Rps2r3 genes are in the grc and have multiple stop codons in their genomic sequences. The Rps2r1 mRNA transcript was identified by RT-PCR in the thymus and testis but not in the liver an d spleen.