GAL11P: a yeast mutation that potentiates the effect of weak GAL4-derived activators

A mutant yeast in which a weak GAL4-derived activator functions as a strong activator bears a single mis-sense mutation in GAL11 (a.k.a. SPT13). The first 74 amino acids of GAL4, including the zinc-dependent DNA binding region, attached to an acidic activating sequence, are sufficient to respond both to GAL11 and to our mutant GAL11P (potentiator). PPR1, a yeast activator with a similar zinc finger sequence, also responds to GAL11 and to GAL11P, whereas regulators bearing unrelated DNA binding motifs do not. GAL11 itself works as a strong activator when tethered to DNA by fusion to the bacterial LexA protein, and deletion of GAL11 is known to cause a 5- to 10-fold reduction in GAL4 activity. We suggest that a complex of GAL4 and GAL11 constitutes a particularly strong activator; evidence that the putative GAL4-GAL11 complex ordinarily forms preferentially on DNA suggests a biological rationale for GAL11 action.     

Amphipathic alpha-helices in proteins: results from analysis of protein structures

Amphipathic alpha-helices play a crucial role in mediating the interaction of peptides and proteins with membranes. We have analyzed protein structures for the occurrence of 18-residue amphipathic helices. We find several of these alpha-helices having average hydrophobic moments and average hydrophobicities that would favor their interaction with membranes. We have analyzed the distribution of net charge, helix length, normalized frequency of occurrence, and propensities of the 20 amino acids in the delineated 18-residue helices. We have observed distinct differences in the frequencies of occurrence of polar and hydrophobic amino acids at positions 1-18 in amphipathic and nonamphipathic helices. There are also differences in propensities of the 20 amino acids to occur at positions 1-18 of amphipathic and nonamphipathic helices. Synthetic peptides corresponding to some of these surface-seeking helices do possess antibacterial and/or hemolytic activities. Knowledge of the distribution of charges in 18-residue surface-seeking amphipathic alpha-helices, as well as propensity of occurrence of amino acids at various positions, would be useful inputs in the de novo design of amphipathic peptides.     

DNA binding is not sufficient for nuclear localization of regulatory proteins in Saccharomyces cerevisiae.

We showed by immunofluorescence that the procaryotic DNA-binding protein LexA and a chimeric protein that contains the DNA-binding portion of LexA (amino acids 1 to 87) and a large portion (amino acids 74 to 881) of the Saccharomyces cerevisiae positive regulatory GAL4 protein (GAL4 gene product) are not preferentially localized in the nucleus in S. cerevisiae.