Conservation of the TRAPPII-specific subunits of a Ypt/Rab exchanger complex.

Background: Ypt/Rab GTPases and their GEF activators regulate intra-cellular trafficking in all eukaryotic cells. In S. cerivisiae, the modular TRAPP complex acts as a GEF for the Golgi gatekeepers: Ypt1 and the functional pair Ypt31/32.

TRAPPII subunits are required for the specificity switch of a Ypt-Rab GEF.

Ypt-Rab GTPases are key regulators of the various steps of intracellular trafficking. Guanine nucleotide-exchange factors (GEFs) regulate the conversion of Ypt-Rabs to the GTP-bound state, in which they interact with effectors that mediate all the known aspects of vesicular transport. An interesting possibility is that Ypt-Rabs coordinate separate steps of the transport pathways.

Phylogenetic analysis of Sec7-domain-containing Arf nucleotide exchangers.

The eukaryotic family of ADP-ribosylation factor (Arf) GTPases plays a key role in the regulation of protein trafficking, and guanine-nucleotide exchange is crucial for Arf function. Exchange is stimulated by members of another family of proteins characterized by a 200-amino acid Sec7 domain, which alone is sufficient to catalyze exchange on Arf. Here, we analyzed the phylogeny of Sec7-domain-containing proteins in seven model organisms, representing fungi, plants, and animals.

Quantitative immunohistochemistry by measuring cumulative signal strength accurately measures receptor number.

We previously demonstrated that quantitative immunohistochemistry (Q-IHC) performed by measuring the cumulative signal strength of the digital file encoding an image can be used to determine the absolute amount of chromogen present per pixel. We now show that Q-IHC so performed can be used to accurately determine the amount of peptide hormone receptor of interest in archived tissues. To do this we transfected Balb 3T3 fibroblasts with the cDNA encoding the human receptor for gastrin-releasing peptide (GRP), and selected six cell lines stably expressing between 10(2) and 10(6) receptors/cell.