The endoplasmic reticulum exit of glutamate transporter is regulated by the inducible mammalian Yip6b/GTRAP3-18 protein

GTRAP3-18 interacts with and reduces the activity of the neuronal specific Na(+)/K(+) glutamate transporter, EAAC1 both in vitro and in vivo. GTRAP3-18 and the related isoform, JM4, are distant relatives of the Rab GTPase-interacting factor PRA1, and share a topology of four transmembrane domains and cytosolic termini. GTRAP3-18 and JM4 are resident endoplasmic reticulum (ER) proteins. The physiological role of GTRAP3-18 is poorly understood. We demonstrate for the first time that GTRAP3-18 is a regulator of ER protein trafficking. Expression of GTRAP3-18 delays the ER exit of EAAC1, as well as other members of the excitatory amino acid transporter family. GTRAP3-18 uses hydrophobic domain interactions in the ER membrane to self-associate and cytoplasmic interactions at the C terminus to regulate trafficking. The features of GTRAP3-18 activity are consistent with recent phylogenic sequence analyses suggesting GTRAP3-18 and JM4 be reclassified as mammalian isoforms of the yeast protein family Yip, Yip6b, and Yip6a, respectively.     

The AtPP gene of the Brassica napus S locus region is specifically expressed in the stigma and encodes a protein similar to a methyltransferase involved in plant defense

Self-incompatibility (SI) in Brassica is controlled by the S locus. The specificity of the SI response is controlled on the stigma side by the S receptor kinase (SRK) and on the pollen side by the SCR (S locus cysteine-rich) protein, but other proteins might be involved in the process of self-pollen rejection. In this study, we show that the AtPP gene linked to the S locus of Brassica napus is expressed in the stigmas of SI lines. AtPP has a developmental pattern of expression similar to the SRK gene. The AtPP protein has similarity with members of an Arabidopsis protein family and with an S-adenosyl-L-methionine:salicylic acid carboxyl methyltransferase, which is a plant defense-related protein of Clarkia breweri representing a new class of methyltransferases. A member of the AtPP gene family is present in the homeolog region of the S locus in Arabidopsis. Therefore, this gene might have co-evolved with S genes from an ancestral S locus of Brassicaceae. Possible functions of the AtPP protein in the self-recognition process are discussed. Received: 9 October 2000 / Revision accepted: 23 April 2001     

CLUTCH SIZES AND BREEDING STRATEGIES AMONG BERMUDAN AND NORTH AMERICAN PASSERINES

Evidence for reduction of clutch size in insular passerines is presented. Average clutch sizes for the Catbird, Cardinal and White-eyed Vireo were reduced 14.0, 18.2 and 30.7%, respectively as compared with coastal North American populations from similar latitudes. Differences are highly significant. Clutch size in the Eastern Bluebird was not reduced. Trends in latitudinal and longitudinal variations of clutch size in North America are examined. With the exception of a slight latitudinal gradient in coastal populations, no consistent trends existed. There is no evidence for reduced variability in clutch size or increased egg size in the Bermudan populations, but both these parameters may show some response to combined effects of latitude and longitude in continental populations.
Reduction of clutch size in insular nidicolous birds is consistent with both the Lack-Ashmole resource limitation hypothesis and Cody's energy allocation hypothesis. In the absence of experimental evidence for life history optimization in response to K-selection, the modified Lack hypothesis seems sufficient.