Commitment to cell division occurs at a point late in the G1 phase of the cell cycle, termed Start. Passage through Start requires the activation of the Cdc28 protein kinase by the cell cycle-regulated G1 cyclins. Maximal expression of these G1 cyclins is induced by the heterodimeric transcription factor complex composed of Swi4 (also designated Art1) and Swi6. Swi4 is the DNA-binding subunit of this complex. In addition to binding Swi4, Swi6 forms a complex with Mbp1. This complex activates S-phase cyclins and genes involved in DNA synthesis Rpb1 is the largest subunit of the yeast RNA polymerase II. Srb4 is a basal transcription factor that is essential for the establishment of the transcription initiation apparatus. Stress factors induce transcription through the induction of various transcription factors. Yap1 activates expression in response to oxidative stress, while Msn2 and Msn4 mediate transcription via the stress response element (STRE).
