Bora is a 61kD member of the Bora family of proteins. It is ubiquitously expressed, and plays a key role in cell cycle progression. Plk1 is a phosphorylase that is important to the cell during the G2/M transition and mitosis. Its activity is initially regulated by Aurora-A, which phosphorylates and activates Plk1 on aa210. Bora, Aurora-A and Plk1 all appear to form a complex during G2. Bora predisposes Plk1 to the actions of Aurora-A. Once activated by Aurora-A, Plk1 drives the mitotic mechanism, which includes a third-party phosphorylation of Bora. This initiates Bora dissociation from Aurora-A with subsequent ubiquitination and degradation. Human Bora is 559aa in length. It contains a Ser-rich region aa188-278 and at least eight utilized Ser phosphorylation sites. Phosphorylation may increase the SDS-PAGE MW of Bora to 75-85kD. There is one potential alternative start site that lies 60aa upstream of the standard start site, and a second splice variant the shows a 17aa substitution for aa1-87. Over aa2-180, human Bora shares 84% aa identity with mouse Bora.