Parallel pathways of gene regulation: homologous regulators SWI5 and ACE2 differentially control transcription of HO and chitinase.

Abstract

Two independent pathways oJ transcriptional regulation that show functional homology have been identified in yeast. It has been demonstrated previously that SWI5 encodes a zinc finger DNA-binding protein whose transcription and cellular localization both are cell cycle regulated. We show that ACE2, whose zinc finger region is nearly identical to that of SWI5, shows patterns of cell cycle-regulated transcription and nuclear localization similar to those seen previously for SMTIS. Despite their similarities, SWI5 and ACE2 function in separate pathways of transcriptional regulation. SWI5 is a transcriptional activator of the HO endonuclease gene, whereas ACE2 is not. In contrast, ACE2 is a transcriptional activator of the CTSl gene (which encodes chitinase), whereas SWI5 is not. An additional parallel between the SWI5/HO pathway and the ACE2/CTS1 pathway is that HO and CTSl both are cell cycle regulated in the same way, and HO and CTSl both require the SWI4 and SWr6 transcriptional activators. Overproduction of either SWI5 or ACE2 permits transcriptional activation of the target gene from the other pathway, suggesting that the DNA-binding proteins are capable of binding in vivo to promoters that they do not usually activate. Chimeric SWI5/ACE2 protein fusion experiments suggest that promoter specificity resides in a domain distinct from the zinc finger domain.

Swi5 Controls a Novel Wave of Cyclin Synthesis in Late Mitosis

“…A second transcription factor, Ace2, is active at about the same time in the cell cycle as Swi5 (Dohrmann et al, 1992), and we therefore also included strains deleted for the ACE2 gene. Expression of PCL9 is absent in a swi5⌬ and in a swi5⌬ace2⌬ strain, whereas in an ace2⌬ strain PCL9 transcript levels seem not to be affected ( Figure 3A).…”

Comprehensive Identification of Cell Cycle–regulated Genes of the YeastSaccharomyces cerevisiaeby Microarray Hybridization

“…GAL-CLN3 may repress some of these genes, whereas GAL-CLB2 has no consistent effect on the expression of these genes. Several of these genes are known to be regulated by the transcription factor Swi5p, which itself is a member of the CLB2 cluster (Dohrmann et al, 1992;Bobola et al, 1996;Knapp et al, 1996). Swi5p is thought to bind to a site with the consensus ACCAGC (Knapp et al, 1996), and indeed, when we searched for common motifs in the 5Ј regions of the SIC1 cluster, we found the consensus RRCCAGCR in many of the 27 genes.…”

Aft1p and Aft2p Mediate Iron-responsive Gene Expression in Yeast through Related Promoter Elements

“…DNA oligonucleotides, with sequences complementary to lacZ, FIT3 and CMD1 mRNA (calmodulin as an internal loading control), were end-labeled with 32 P using T4 polynucleotide kinase (New England Biolabs). S1 analysis was carried out as previously described (1). Briefly, the 32 P-labeled oligonucleotides were hybridized with 12 g of total RNA in HEPES buffer (38 mM HEPES, pH 7.0, 0.3 M NaCl, 1 mM EDTA, 0.1% Triton X-100) at 55°C overnight.…”

“…Included in this group are Ace2p/Swi5p, Pdr1p/ Pdr3p, and Yap1/Yap2p. Ace2p and Swi5p regulate the expression of cell cycle-specific genes, are 83% identical in their zinc finger DNA-binding domains and recognize the same DNA binding site in vitro (1,2). However, Ace2p and Swi5p can regulate separate genes, where discrimination between promoter elements is achieved through the interaction of these factors with other DNA-binding proteins (2).…”