HUMAN-IMMUNODEFICIENCY-VIRUS FITNESS IN-VIVO - CALCULATIONS BASED ON A SINGLE ZIDOVUDINE RESISTANCE MUTATION AT CODON-215 OF REVERSE-TRANSCRIPTASE

We monitored a subject newly infected with a zidovudine-resistant huma n immunodeficiency virus type 1 strain and found that in the absence o f drug, the viral population with the resistance conferring tyrosine ( TAG) codon 215 of reverse transcriptase was gradually replaced. By usi ng standard formulas to model the effects of selection at a single loc us in an asexual haploid population, the relative fitness gain of the viral population with a single mutation at codon 215 creating a serine (TCC) was calculated. We concluded that a viral population with a ser ine at reverse transcriptase codon 215 conferring zidovudine sensitivi ty was between 0.4 and 2.3% more fit.