PLK1 mRNA spans approximately 11.5 kb and has 10 exons. The sizes of the exons 1 to 10 are 461, 169, 145, 94, 220, 156, 78, 155, 183 and 508 bps.

PLK1 mRNA (NM_005030) is 2204 bp. PLK1 expression is believed to reach its peak value in mitosis in the cell cycle. It is highly expressed in actively proliferating tissues such as those in the placenta, spleen, ovary, and testis. High expression of PLK1 is also detected in various neoplastic tissues. Northern blot analysis reveals low or undetectable levels of PLK1 transcript in most other adult tissues (e.g.: brain, thymus, liver, lung, pancreas, heart, kidney, stomach, intestine and skin).

Mouse Plk gene maps to Chromosome 7 and the processed pseudogene to mouse Chromosome 5. No human pseudogene for PLK1 has been reported.

Protein consists of 603 amino acids and is 66kDa. In addition to the N-terminus kinase domain, there are two conserved polo-box regions of 30 amino acids at the C-terminus. Kinase activity is regulated at least in part, by the polo-boxes that are functionally important for both auto-inhibition and sub-cellular localization.

PLK1 protein becomes a target of the anaphase-promoting complex/cyclosome and is degraded by the ubiquitin-proteasome pathway as cells exit mitosis.

During interphase, PLK1 localizes to centrosomes. In early mitosis, it associates with mitotic spindle poles. A recombinant GFP-PLK1 protein localizes to centromere/kinetochore region, suggesting a possible role for chromosome separation.

PLK1 is believed to be involved in the regulation of key steps during cell division, DNA damage repair pathways, apoptosis, and the progression of the cell cycle.
PLK1 has roles in the activation of cdc2 through cdc25 and direct phosphorylation of cyclin B1, through which MPF (mitosis promoting factor) is activated so that mitosis can start.
Microinjection of PLK1 antibodies causes failure of g-tubulin recruitment to the centrosomes. This failure results in immature centrosomes and monopolar spindle formation. Similar microinjection experiments in cell lines (transformed HeLa and non-immortalized Hs68 fibroblasts) result in a marked inhibition of cell cycle progression.
PLK1 also has a possible role during cytokinesis based on the observation that PLK1 interacts and co-localizes with a kinesin related motor protein (CHO1/MKLP-1) at the interzone during anaphase and the mid-body during telophase and cytokinesis.
Evidence suggests that BRCA2 is a substrate of PLK1 both in response to DNA damage and during normal cell cycle progression. This suggests a role for PLK1 in regulating DNA damage repair.
Other studies have shown that the loss of PLK1 expression can induce pro-apoptotic pathways and inhibit growth.
Based on yeast and murine studies of meiosis, human PLK1 may also have a regulatory function in meiosis. S. cerevisiae polo kinase CDC5 is required to phosphorylate and remove meiotic cohesion during the first cell division. In CDC5 depleted cells, kinetochores are bioriented during meiosis I, and Mam1, a protein essential for coorientation, fails to associate with kinetochores. CDC5 is believed to have roles in sister-kinetochore coorientation and chromosome segregation during meiosis I..

P.troglodytes: PLK1, polo-like kinase, XP_510879.1, 735 aa
M.musculus: Plk1, polo-like kinase 1 (Drosophila), NP_035251.2, 603 aa
R.norvegicus: Plk1, polo-like kinase 1 (Drosophila), NP_058796.1, 603 aa
D.melanogaster: polo, polo, NP_524179.2, 576 aa
C.elegans: plk-1 PoLo Kinase, NP_741243.1, 649 aa
S.cerevisiae: CDC5, NP_013714.1, 705 aa