Fig. 6.

The high molecular weight keratin species observed in the presence of 16E1^E4 are ubiquitylated. (A,B), SiHa cells expressing 16E1^E4 or β-Gal were harvested and lysed 24 hours after infection; keratin was immunoprecipitated using either C2562, a pan-keratin antibody (A) or L2A1, a K8-K18 antibody (B). A ubiquitin probe of the immunoprecipitates reveals accumulation of high molecular weight ubiquitylated keratin, Ub-K (panels i). High molecular weight K18 laddering was also apparent in K18 probed cell extracts. IPs reprobed for K18 revealed that these ladders were immunoprecipitated, indicating that they are ubiquitylated (panels ii). Alignment of the IPs probed with K18 and ubiquitin identified a number of discrete bands, common to both blots, thus confirming the presence of ubiquitylated K18 in 16E1^E4-expressing cells (panels iii).