Jf. Partridge et al., CELL CYCLE-DEPENDENT TRANSCRIPTION OF CLN1 INVOLVES SWI4 BINDING TO MCB-LIKE ELEMENTS, The Journal of biological chemistry, 272(14), 1997, pp. 9071-9077
Two promoter elements have been defined that activate G(1)/S-specific
transcription in Saccharomyces cerevisiae. SCB elements (CACGAAA) are
activated by the Swi4-Swi6 complex, and RICH elements (ACGCGTNA) are a
ctivated by the Mbp1-Swi6 complex. CLN1 encodes a cyclin which is expr
essed during this interval, and requires Swi4 and Swi6 for peak transc
ription, but it has no consensus SCB elements in its promoter. Two SCB
-like sequences had been previously noted and suggested to be the func
tional promoter elements. Our studies indicate that these sequences ar
e unable to activate transcription of a lacZ reporter construct, or to
bind Swi4-Swi6 complexes in vitro, However, a cluster of three sequen
ces resembling MCB sequences are active promoter elements, sufficient
to confer G(1)/S-specific transcription to a reporter. These sites are
the predominant activation elements in the CLN1 promoter, and despite
their resemblance to MCB elements, they bind Swi4-Swi6 complexes in v
itro and require Swi4 and Swi6 for their activity in vivo. This indica
tes that the sequences that promote Swi4/Swi6 binding have not been fu
lly defined, or that there are multiple Swi4- and Swi6-containing comp
lexes with distinct DNA binding specificities. In addition to these no
vel Swi4/Swi6-binding sites, these studies also show that there must b
e at least one novel promoter element that can confer G(1)/S-specific
transcription to CLN1, because when all the potential SCB- and MCB-lik
e sequences are eliminated the transcript is still cell cycle regulate
d.