TABLE 1.

Subunits of P-TEFb

Source and subunit	Apparent/actual length (kDa)	Species (reference)a
Insect
Cdk9	43/46.8	D (85)
Cyclin T	124/118	D (58)
Cyclin K	NDc	D (17)
Mammalian
Cdk9	41/42.8b	H (30, 85)
Cyclin T1	87/80.7b	H (59, 72); M (7, 23); E (6); C (67)
Cyclin T2a	78/73.7b	H (59)
Cyclin T2b	90/81.1b	H (59)
Cyclin K	50/41.3b	H (17, 20); M (17)

^aD, Drosophila; H, human; M, mouse; E, equine; C, canine. 

^bSource, human. 

^cND, not determined.