FIGURE 4.

Telomerase activity, hTR, and TCAB1 levels do not change over the cell cycle. A, HeLa cells were released from a double thymidine induced G₁/S block, and cells were harvested at time points as the cell cycle progressed. Telomerase activity was assayed by QTRAP, with values set relative to t = 0 at the G₁/S block (n = 4). Total hTR was measured by RT-qPCR. Values were normalized to GAPDH mRNA and set relative to t = 0 (n = 3). B, total endogenous TCAB1 protein from HeLa cells synchronized by double thymidine block was measured by immunoblot and quantified relative to tubulin protein (n = 5). All lanes were from the same blot; a gap indicates removal of extraneous samples. C, HaCaT cells were synchronized at G₁/S by double thymidine block. Telomerase activity was measured by QTRAP with values set relative to the t = 0 time point (n = 3). async, asynchronous cell cultures. n.s., not significant.