Identification of a Rps12 pseudogene, pS12X. (A) Alignment of the longest expressed sequence tag corresponding to mouse ribosomal protein S12 cDNA (GenBank accession no. AI526798) and pS12X (bp 3,015–2,472 of GenBank accession no. AJ010350) sequences. Direct repeats (DR) are in grey boxes. Poly(A) stretch is found immediately before the 3′ direct repeat. CJ10–CJ12 primer locations are indicated by arrows. CJ9 is located outside of known Rps12 expressed sequence tags and cDNA sequence. (B) Tissue distribution of the CJ11–CJ12 RT-PCR product. Total RNA from male (M) or female (F) ES cells, adult fibroblasts (Fib), brain (B), and liver (L) was reverse transcribed by random priming and amplified with primers CJ11 and CJ12. −RT controls were processed in parallel without adding RT. (C) Northern blot analysis of total ES and fibroblast RNA with a pS12X probe. ES cells are male (J1, 40XY), female (EL16, a mosaic cell line: 30% 40XX and 70% 39XO), and transgenic (Tg, 116.6).