Abstract
Following amplification by PCR of a portion of the matrix phosphoprotein pp150 gene, electrophoretic analysis revealed the simultaneous presence of two viral variants of human cytomegalovirus in the blood of a heart transplant recipient. Repeated denaturation- annealing cycles during the amplification reaction led to the formation of heteroduplex molecules with altered electrophoretic mobility. Sequence analysis of the amplification products showed the presence of a viral variant carrying an in-frame three nucleotide deletion, which caused the absence of an aspartic acid in the corresponding protein. Attempts to plaque-purify the deletion mutant were unsuccessful, suggesting that the variant was growth-defective.