Figure 4: Levels of CCR5 mRNA. Northern analyses were carried out using RNA isolated from parental PM1 cells (—, lanes 4 and 8) and cell lines that expressed TK1 (lanes 1 and 5), C2 (lanes 2 and 6), and C1 (lanes 3 and 7). Equal amounts of each RNA sample (30 μg) were separated on agarose gels that contained formaldehyde, transferred to nitrocellulose membranes, and hybridized to a -radiolabeled probe that contained the actin (lanes 1–4) and CCR5 mRNA sequences (lanes 5–8).