Genome analysis of Marek's disease virus strain CVI-988: Effect of cell culture passage on the inverted repeat regions

The genomes of different derivatives of Marek's disease virus (MDV) strain CVI-988, a low oncogenic isolate of a serotype 1 MDV, were analyzed by rest riction enzyme analyses to detect whether alterations occurred after passag es in cell culture. DNA molecules of strain 988 isolated directly from bloo d cells contained mainly two copies of the 132-bp repeat sequence previousl y reported within BamH1-H and -D fragment as previously reported for more v irulent MDV strains. Although a minority of virus particles showed repeat a mplification was already at the fifth passage level, amplification mainly o ccurred between passages 17 and 34 in cell culture. In addition, a 400-bF d eletion was detected within the BamH1-A fragment of two derivatives of CVI- 988, 988C and 988C/R6.