Rat lens beta-crystallins are internally duplicated and homologous to gamma-crystallins

The nucleotide sequence of two cloned rat lens beta-crystallin cDNAs pRL beta B3-2 and pRL beta B1-3 has been determined. pRL beta B3-2 contains the complete coding information for a beta-crystallin, designated beta B3, of 210 amino acid residues. pRL beta B1-3 is incomplete at its 5' end; the 5' codogenic information which is not present in this cDNA clone was deduced from the cloned gene. pRL beta B1-3 codes for a beta-crystallin polypeptide, designated beta B1, whose full length is 247 amino acid residues. Considerable sequence homology is noted between the amino- and carboxy-terminal halves of each protein. The two rat beta-crystallins show a substantial sequence homology with each other (60%) as well as with the published sequences of rat gamma-crystallin (37%) and bovine and murine beta-crystallins (55 and 45%). All these proteins have a two-domain structure which, like the bovine gamma II-crystallin, might be folded into four remarkably similar protein motifs. Our data further indicate that the beta-crystallins can be subdivided into two groups which are evolutionarily related. Both groups are, although more distantly, also related to the gamma-crystallins.     

Recognition of influenza virus hemagglutinin by subtype-specific and cross-reactive proliferative T cells: contribution of HA1 and HA2 polypeptide chains

The recognition of influenza virus hemagglutinin (HA) by T lymphocytes was examined by assaying the T cell proliferative response of influenza virus-primed T cells to purified HA of different influenza A subtypes or to isolated heavy (HA1) or light (HA2) polypeptide chains of the HA molecule. The proliferative response to HA was dependent on the activation of an Ly-1+2- subset of T cells and required the presence of nylon wool-adherent, radiation-resistant accessory cells. T cells from mice primed by infection with one strain of type A influenza virus cross-reacted with other purified HA not only of the same subtype as the priming virus but also of serologically distinct subtypes of influenza A (but not B) virus. The response of virus-primed T cells to the homologous HA or to HA of the same subtype was shown to involve recognition of determinants on both the HA1 and the HA2 chains. The recognition of HA of different subtype by cross-reactive T cells appeared to be directed predominantly to determinants on HA2. Because the antibody response to influenza virus HA is not cross-reactive between subtypes and is directed predominantly to determinants on HA1, the present results indicate that at least some of the determinants on HA recognized by T cells are different from those recognized by B cells and that the HA2 chain may be involved primarily in stimulation of T cell rather than B cell immunity.     

Strain difference in the radiosensitivity of immunocompetent cells and its influence on the residual host-vs-graft reaction in lethally irradiated mice grafted with semiallogeneic bone marrow

A striking difference in radiosensitivity was noted between C3H/He (H-2k) and C57BL/6J (H-2b) strain mice when assessed by primary anti-SRBC PFC response of intact animals and primary cell-mediated lympholysis (CML) response of spleen cells to allogeneic cells in vitro, the C3H strain being more radioresistant. On the other hand, when C3H and B6 mice were exposed to 6.62 to 10.40 grays (Gy) of x-rays and then were transplanted with 2 X 10(6) bone marrow cells from B6C3F1 (H-2b/k) donor mice within 3 hr or at 24 hr after radiation exposure, the early mortality caused by residual host-vs-graft (HVG) reaction was much higher when C3H mice were used as recipients. Furthermore, the proportion of surviving animals manifesting host-type lymphohemopoiesis, i.e., host-type revertants, was much higher in B6C3F1 to C3H than in B6C3F1 to B6 combination. Spleen cells from such host-type revertants manifested strong anti-donor reactivity when assessed by mixed lymphocyte reaction (MLR) and/or CML in vitro. Increase of radiation doses to the recipients to 10.40 Gy resulted in 100% survival and 100% donor-type lymphohemopoiesis in both groups of chimeras. These results indicate strongly that a genetic difference in radiosensitivity of immune system of the recipients can greatly influence the magnitude of residual HVG reactions observed in hybrid to parental strain bone marrow transplantation in mice.     

Superoxide perturbation of the organization of vascular endothelial cell membranes

Cultured porcine thoracic aorta endothelial cells were covalently labeled with 4-maleimido-2,2,6,6-tetramethylpiperidinooxyl. Electron paramagnetic resonance spectrometry revealed two major binding environments representing strongly and weakly immobilized species. The disorder parameter of weak/strong, determined from the respective peak amplitudes, was irreversibly elevated following incubation of endothelial cells with a superoxide-generating system, indicating increased membrane fluidity. The rate of increase in membrane disorder was dependent upon superoxide generation rates. Incorporation of the spin-label at concentrations less than 250 microM had no effect on cell viability. The cellular proteins reacting with the spin-label were predominantly membrane proteins, characterized by immunoblotting using a rabbit anti-4-maleimido-2,2,6,6-tetramethylpiperidinooxyl IgG, following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophorectic transfer to nitrocellulose.     

Magnesium effects on activation of skinned fibers from striated muscle

The intracellular Ca movements that control contraction and relaxation of striated muscle are regulated by the membrane potential and influenced by Mg2+. In skinned fibers, the internal composition can be manipulated directly by Ca movements estimated from isometric force transients, net changes in sarcoplasmic reticulum (SR) Ca, and 45Ca flux between fiber and bath. Stimulated Ca release, unlike unstimulated 45Ca efflux at low external [Ca2+], is highly [Mg2+]-sensitive at 20 C. Force and tracer measurements indicate three major sites of Mg2+-Ca2+ interaction in situ: Mg2+ can stimulate the SR active Ca transport system, inhibit a Ca2+-dependent Ca efflux pathway of SR, and shift the force-[Ca2+] relation, presumably by reducing Ca2+ binding to myofilament regulatory sites. These mechanisms constrain the resting Ca flux and are adaptive during relaxation. However, analysis of CI-stimulated 45Ca release and reaccumulation suggests that the depolarization process may inhibit Mg2+-dependent Ca influx, the membrane potential controlling both efflux and influx; recent studies on voltage-clamped cut fibers support this hypothesis. The Ca2+ and Mg2+ dependence of caffeine-stimulated 45Ca efflux suggests that Mg2+ inhibition of the Ca2+-dependent efflux pathway is small during rapid Ca2+ efflux. Therefore, both Mg2+ mechanisms, which minimize net release, may be reversed during normal activation.     

Growth-dependent expression of a cell surface glycoprotein

The expression of the hepatocellular membrane receptor for desialylated galactose-termining glycoproteins was studied during different proliferative stages of a human hepatoma cell line. Rapidly growing cells exhibited a reduced endocytotic rate of desialylated orsomucoid as compared to non-growing cells. This reduction was shown to be the consequence of a lower concentration of active cell-surface associated receptor protein in the dividing cells.