CHARACTERIZATION OF 2 DISTINCT GENE TRANSCRIPTS FOR RIBOSOMAL-PROTEIN-L21 FROM PATHOGENIC AND NONPATHOGENIC STRAINS OF ENTAMOEBA-HISTOLYTICA

A second gene (rp-L21) copy clone g34, coding for ribosomal (r-) prote in L21, was isolated from the pathogenic (P) strain HM-1:IMSS c16 of t he intestinal parasite Entamoeba histolytica (Eh). The gene was compar ed to the previously isolated copy, gLE3 [Petter et al., Mel. Biochem. Parasitol. 56(1992) 329-334], with respect to its primary structure, mRNA levels and binding to the r-complex during translation. Unlike th e gLE3 gene copy [Petter et al., Mel. Biochem. Parasitol. 56(1992) 329 -334], g34 was found not to be physically connected to an actin gene c opy. Homologous copies of the two rp-L21 genes were also characterized from the nonpathogenic (NP) strain SAW1734R clAR, as well as from its P derivative. Sequence comparison of the coding regions of the two rp -L21 revealed almost full identity. Significant differences were found , however, within their 3' and 5' flanking regions. Using the 3' rapid amplification of cDNA ends (3' RACE) method [Frohman et al., Proc. Na tl. Acad. Sci. USA 85 (1985) 8998-9002], as well as Northern and slot blot hybridizations, it was demonstrated that both rp-L21 mRNAs are fo und in similar amounts. However, as was shown by differential hybridiz ation, the relative binding of each transcript to the r-complex varied somewhat between P and NP strains. This finding suggests that the con trol of expression of rp-L21 in Eh may involve regulation at the post- transcriptional level.