Northern blot analyses of UL144 transcripts. RNA preparations from HCMV clinical strains H, Ch and Xu in immediately early (IE), early (E) and late (L) kinetics classes were used in this analysis. RNA from non-infected HELF cells (Z) was used as a negative control. The Northern blot was performed with three different probes, produced according to the sequences of the three different isolates using 144For2 and 144Prob primers. The four UL144 transcripts are indicated by arrows. The positions of RNA size markers are indicated.