sentence1: It has been shown, however, that ubiquitination of cyclin D1 can efficiently take place following phosphorylation of another site, or without the apparent requirement for phosphorylation.
sentence2: APC-dependent degradation of cyclin D1 does not require threonine 286 phosphorylation, but the presence of a “cyclin degradation box”, however, as observed in the present study, threonine 286 phosphorylation is essential for proteolytic degradation of cyclin D1 in skin