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Functional divergence between the half-sites of the DNA-binding sequence for the yeast transcriptional regulator Rap1p.

ABSTRACT: The yeast transcriptional regulator Rap1p binds to the DNA consensus sequence ACACCCAYACAYYY. We have previously shown that DNA-binding sites in which all four Y (Y=T or C) positions were Ts (UASrpg sequences) synergized more efficiently to activate transcription than sequences in which all Ys were Cs (telomere sequences) [F.-Z. Idrissi, J. Fernández-Larrea and B. Piña (1998) J. Mol. Biol. 284, 925-935]. Here we provide evidence that the DNA consensus sequence for Rap1p behaves as a combination of two ACAYYY half-sites with different functionality, the presence of Ts in the second half-site being the determinant for the transcriptional behaviour of the UASrpg sequences. DNA structure in the different complexes with Rap1p varied from being relatively uniform to appear rather distorted, this also being dependent on the presence of Ts in the second half-site. These distortions did not cause sharp bends or kinks in the DNA molecule. Computer analysis suggests that high-affinity binding of Rap1p to UASrpg sequences requires a rearrangement of the C-terminal Myb domain of the protein. We propose that the structural alterations in Rap1p-DNA complexes, both in the DNA and in the protein, affect the transcription potential of the complex in an allosteric manner. We also propose that the dimeric nature of the Rap1 DNA-binding domain is a key structural feature that explains the disparate functions of its DNA-binding sites in vivo.

SUBMITTER: Idrissi FZ

PROVIDER: S-EPMC1220382 | biostudies-other | 1999 Aug

REPOSITORIES: biostudies-other

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Project description:Despite over a billion years of evolutionary divergence, several thousand human genes possess clearly identifiable orthologs in yeast, and many have undergone lineage-specific duplications in one or both lineages. These duplicated genes may have been free to diverge in function since their expansion, and it is unclear how or at what rate ancestral functions are retained or partitioned among co-orthologs between species and within gene families. Thus, in order to investigate how ancestral functions are retained or lost post-duplication, we systematically replaced hundreds of essential yeast genes with their human orthologs from gene families that have undergone lineage-specific duplications, including those with single duplications (1 yeast gene to 2 human genes, 1:2) or higher-order expansions (1:>2) in the human lineage. We observe a variable pattern of replaceability across different ortholog classes, with an obvious trend toward differential replaceability inside gene families, and rarely observe replaceability by all members of a family. We quantify the ability of various properties of the orthologs to predict replaceability, showing that in the case of 1:2 orthologs, replaceability is predicted largely by the divergence and tissue-specific expression of the human co-orthologs, i.e., the human proteins that are less diverged from their yeast counterpart and more ubiquitously expressed across human tissues more often replace their single yeast ortholog. These trends were consistent with in silico simulations demonstrating that when only one ortholog can replace its corresponding yeast equivalent, it tends to be the least diverged of the pair. Replaceability of yeast genes having more than 2 human co-orthologs was marked by retention of orthologous interactions in functional or protein networks as well as by more ancestral subcellular localization. Overall, we performed >400 human gene replaceability assays, revealing 50 new human-yeast complementation pairs, thus opening up avenues to further functionally characterize these human genes in a simplified organismal context.

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Functional divergence between the half-sites of the DNA-binding sequence for the yeast transcriptional regulator Rap1p.

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