The secondary structure determination has confirmed our prediction that Hsdim1p and thioredoxin fold similarity. To gain additional insight into Dim1p activity, we used HsDim1p as a bait in a two-hybrid screening and isolated specific partner proteins that were previously defined as regulators of splicing, as well as a novel protein, Dimit. Dimit is predominantly expressed in the nucleus. Of note, while it is distributed throughout the nucleus, a significant proportion of detectable Dimit is present in nuclear speckles that colocalize with the SC35 antigen, further supporting the idea of association with splicing complexes. Our current hypothesis is that Dimit, like HEF1, may be a substrate for Dim1p activity.
Functional studies are in progress.
We have begun to further characterize these genes in relationship to the well-conserved signaling control pathways between humans and yeast. To date, we have been able to sort the human genes into a number of discrete functional groups by such approaches. Focusing on HEIC and HEI10 in particular, we are currently engaged in characterizing the function of these proteins in mammalian cells. Our findings provide an explanation for the selection of some proteins as false positives, and have additional implications for potential indirect effects of protein overexpression on transcription in other biological systems. In the new reagent system, termed Dual Bait, a single strain of yeast contains two separately responsive reporter systems.