The initiation translation factor eIF-4A of Cryptosporidium parvum is encoded by two distinct mRNA forms and shows DNA sequence polymorphism distinguishing genotype 1 and 2 isolates

The eukaryotic translation initiation factor eIF-4A is an ATP-dependent RNA helicase involved in ribosome attachment to the 5' end of mRNAs. Employing as a probe a Cryptosporidium parvum genomic amplicon encoding a partial po lypeptide related to eIF-4A, we screened a C. parvum sporozoite cDNA librar y to clone the full length of the gene. Two complete cDNAs were characteriz ed, Cp.F6 and Cp.F10, which consisted of 1,900 and 1,418 bp, respectively. The overlapping portions of the sequences shared 100% identity and encoded a polypeptide of 405 amino acids whose identity to known eIF-4A molecules r anged between 77 and 39%. The 2 cDNAs differed in the length of their respe ctive 3' untranslated regions, of 577 bp in Cp.F6 and 72 bp in Cp.F10, in b oth of which a putative polyadenylation signal was identified. The structur e of the cloned cDNAs, along with genomic Southern blot data indicating tha t eIF-4A is encoded by a single copy gene, strongly suggested that Cp.F6 an d Cp.F10 reflect a differential 3' end processing of mRNA precursors, not o bserved so far in C. parvum. Northern blot analysis confirmed that the spor ozoites express 2 eIF-4A mRNAs and showed that the lower molecular weight t ranscript is 10- to 20-fold more abundant. We also investigated the polymor phism of the eIF-4A gene and defined a novel polymerase chain reaction-rest riction fragment length polymorphism marker discriminating between C. parvu m isolates of genotypes 1 and 2.