Isolation, sequence and molecular karyotype analysis of the actin gene of Cryptosporidium parvum

Actin is an ubiquitous and highly conserved microfilament protein which is hypothesized to play a mechanical force-generating role in the unusual gliding motility of sporozoan zoites and in their active penetration of host cells. We have identified and isolated an actin gene from a Cryptosporidium parvum genomic DNA library using a chicken β-actin cDNA as an hybridization probe. The nucleotide sequences of two overlapping recombinant clones were identical and the amino acid sequence deduced from the single open reading frame was 85% identical to the P. falciparum actin I and human γ-actin proteins. The predicted 42 106-Da Cryptosporidium actin contains 376 amino acids and is encoded by a single-copy gene which contains no introns. The nucleic acid coding sequence is 72% biased to the use of A or T in the third position of codons. Chromosome-sized DNA released from intact C. parvum oocysts was resolved by OFAGE into 5 discrete ethidium bromide-staining DNAs ranging in size from 900 to 1400 kb; the cloned C. parvum actin gene hybridized to a single chromosomal DNA of approximately 1200 kb.