Characterisation of genes encoding a nucleoside monophosphate kinase and a L35 ribosomal protein from Babesia bovis

We have sequenced a region of the Babesia bovis nuclear genome that encodes a L35 ribosomal protein homologue (bl35) and a putative nucleoside monophosphate kinase (bnmk) that is most similar to the adenylate kinase of gram-positive bacteria and the mitochondrial form of adenylate kinase in eukaryotes. BNMK appears to be unique in that it is the first eukaryotic family member to feature a putative zinc-binding domain. bnmk and bl35 are closely linked and transcribed from opposite DNA strands. Examination of the gene structures indicate that the coding regions contain small intervening sequences that obey the GT-AG rule of eukaryotic spliceosomal introns. The single intron separates the bl35 initiation codon from the remainder of the coding region and the 6-exon bnmk gene does not appear to be differentially spliced. Both genes utilise multiple polyadenylation sites and the canonical mammalian polyadenylation signal AATAAA is absent from their 3' untranslated regions. Primer extension analyses reveal that the bnmk gene utilises a cluster of transcription start points, one of which is used most frequently. The bnmk mRNA 5' end does not appear to be cis- or trans-spliced. We report here the first evidence of intronic sequences, as well as heterogeneous 5' and 3' ends for mRNA of a member of the Babesia genus.