The unique histone H2A gene of Aspergillus nidulans contains three introns

The histone H2A gene of the filamentous fungus Aspergillus nidulans has been cloned and sequenced. There is a single H2A gene in the genome of A. nidulans, and it contains three introns. The introns are 51 nucleotides (nt), 56 nt and 50 nt in length and split codons for amino acids (aa) 18, 48 and 116 of the predicted protein. The transcriptional start and termination points have been determined using an S1 nuclease protection assay. The predicted protein is 132 aa residues in length and surprisingly has a threonine after the initiator methionine instead of the usual serine. The sequence of the predicted histone H2A protein is compared to histone H2A proteins from Schizosaccharomyces pombe, Saccharomyces cerevisiae and calf thymus. Comparison of the amino acid sequence to these other H2A proteins shows that the divergence of amino acid sequences between H2A proteins is found in two clustered sites.