Identification and characterization of a prevacuolar compartment in stigmas of nicotiana alata

The stigmas of the ornamental tobacco plant Nicotiana alata accumulate large quantities of a series of 6-kD proteinase inhibitors (PIs) in the central vacuole that are derived from a 40-kD precursor protein, Na-PI. The sorting information that directs Na-PI to the vacuole is likely to reside in a C-terminal propeptide domain of 25 amino acids that forms an amphipathic alpha helix. Using cell fractionation techniques, we have examined transit of Na-PI through the endomembrane system and have identified a prevacuolar compartment that contains Na-PI with an intact targeting signal. In contrast, the targeting signal is not present on the predominant form of Na-PI in the vacuole. The prevacuolar compartment is marked by the presence of homologs of both the t-SNARE, PEP12p, and the putative vacuolar sorting receptor BP-80. Cross-linking and affinity precipitation studies revealed that Na-PI associates with BP-80 within this compartment, providing in vivo evidence for the function of BP-80 as a sorting receptor for a protein with a C-terminal vacuolar targeting signal.     

Biochemical genetics of TL antigens

TL antigens are class I glycoproteins which are expressed on thymocytes and which are coded by the Tla region of the major histocompatibility complex of the mouse. Biochemical analysis of TL molecules from different strains of mice revealed structural variation determined by the Tla region which is detectable by peptide mapping, isoelectric focusing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two-dimensional gels, and by differential reactivity of allelic forms of TL molecules with a panel of anti TL reagents. The quantity of TL expressed on thymocytes is also influenced by the Tla region; three quantitative phenotypes were identified: high (Tla ^a, Tla ^d, Tla ^c), intermediate (Tla ^c, Tla ^f), and low (Tla ^b). (Relative amounts: 1000 : 100 : 1.) Some thymic leukemias arising in (Tla ^b, Tla ^c, Tla ^c) mice with genetically determined reduced levels of thymic TL were found to express TL molecules which were structurally indistinguishable from TL isolated from thymocytes but were present in larger amounts. This suggests that TL structural genes are intrinsically capable of full expression in all mice but that the Tla region of mice expressing an intermediate or low quantity of TL is marked by some feature which causes the thymocyte to express less than the full amount of TL possible.     

Repeated post-exercise administration with a mixture of leucine and glucose alters the plasma amino acid profile in Standardbred trotters

Background  

The branched chain amino acid leucine is a potent stimulator of insulin secretion. Used in combination with glucose it can increase the insulin response and the post exercise re-synthesis of glycogen in man. Decreased plasma amino acid concentrations have been reported after intravenous or per oral administration of leucine in man as well as after a single per oral dose in horses. In man, a negative correlation between the insulin response and the concentrations of isoleucine, valine and methionine have been shown but results from horses are lacking. This study aims to determine the effect of repeated per oral administration with a mixture of glucose and leucine on the free amino acid profile and the insulin response in horses after glycogen-depleting exercise.     

Mating preference tests with the recombinant congenic strain BALB.HTG

Tests of MHC-associated mating preference were conducted with the congenic mouse strains BALE (H-2 ^d), BALB.B (H-2 ^b), and BALB.HTG (recombinant ofH-2 ^d andH-2)^b. The results conform to a hypothesis that anRi gene (Ri-1), the expression of which influences mating preference in females, is situated to the right of theS region; and that anotherRi gene (Ri-2), the expression of which influences mating preference in males, is situated elsewhere, probably to the left ofH-2D. This hypothesis is consistent with conclusions previously reached from study of the mating preferences of B6 and B6-Tla^a congenic mice.Abbreviations according to Yamazaki et al. (1978) Ri recognition of identity     

Relation of gp70 to spontaneous cytolytic activity of mouse spleen cells

In comparing spleen cells of inbred and congenic mice for spontaneous capacity to lyse cells of the BALB/c leukemia RLc1 in vitro, we found that the activity of 129 spleen cells was more than double that of 129-G_ix ^– spleen cells. The only known difference between these two strains is that 129-G_ix ^– mice express no known demonstrable gp70 or p30, whereas 129 mice express both these MuLV-related components as mendelian traits not associated with the production of virions. We infer that MuLV-related components at the cell surface are concerned in effector-target interactions leading to cytolysis under the conditions described. — Although the congenic strains B6 (G_ix ^–) and B6-G_ix ⁺ differ likewise in expression of the type-variant G_ix-gp70, both strains express a second type-variant of gp70. The lytic activity of spleen cells of these two strains for RL1 cells was equally high, suggesting that involvement in lytic effector-target interactions is common to gp70 molecules in general. — When used as targets rather than as effectors 129 spleen cells were more sensitive to lysis than 129-G_ix ^– spleen cells. Pre-exposure to gp70, purified from R-MuLV, rendered splenic effector cells less lytic. Pre-exposure to gp70 also rendered RL1 target cells less sensitive to lysis. One explanation of these findings is that both target cells and effector cells express gp70 and also receptors for gp70 and that this is the basis of mutual cellular recognition leading to lysis in the circumstances described.