The role of the cysteine-rich region of the β2 integrin subunit in the leukocyte function-associated antigen-1 (LFA-1, αLβ2, CD11a/CD18) heterodimer formation and ligand binding

The cysteine-rich region (CRR) of the β2 integrin subunit was replaced by that of β1 to give the chimera β2NV1. β2NV1 can combine with αL to form a variant leukocyte-function-associated antigen (LFA)-1 on COS cell surface, suggesting that the specificity of the β2 interaction with αL does not lie in the CRR. Unlike those expressing wild-type LFA-1, COS cells expressing αLβ2NV1 are constitutively active in intercellular adhesion molecule (ICAM)-1 adhesion. These results suggest that activation of LFA-1 involves the release of an intramolecular constraint, which is maintained, in part, by the authentic β2 CRR.     

A Novel Algorithm for Identification of Activated Cryptic 5′ Splice Sites

Abstract

The resonances of the protonated carbons of [d(TAGCGCTA)]₂ have been assigned by the two-dimensional proton-detected double-quantum heteronuclear correlation experiment ([¹H-^l3C]-DQCOSY). ¹³C-coupled and ^l3C-decoupled versions of the experiment were used. The assignment method is discussed in detail. The deoxyribose cross peaks segregate into five well-resolved regions, and the base cross peaks have distinct features that are helpful for assignments. The cross peaks from the ¹H-¹³C pairs at the Cyd5, Ado2 and ThdCH₃ base positions fall in separate regions of the spectrum from each other; they also are resolved from the closely spaced Ado8, Guo8, Cyd6 and Thd6. Additional parameters for distinction of the base signals are their differing J-coupling values and long-range coupling patterns.     

A developmental study of rat sperm and testis selenoproteins

Essentially all of the selenium in the rat spermatozoon is bound to a polypeptide of Mr 15,000-17,000 confined to the capsule that surrounds the sperm mitochondria. Isoelectric focussing of isolated 75Se-labelled, carboxymethylated mitochondrial capsule protein (MCP) reveals the presence of at least four radioactive components, with a predominant charge isomer at pI4.6. The sperm selenoprotein appears to be identical with MCP, as judged by the exact coincidence of radioactivity and protein stain during two-dimensional electrophoresis. The temporal pattern of 75Se-labelling of rat caput epididymal spermatozoa after intratesticular 75Se injection suggests that maximum incorporation of 75Se into MCP occurs in step 7-step 12 spermatids and that 75Se uptake ceases during step 15 of spermiogenesis. The developmental appearance of sperm selenoprotein in rat testis therefore appears to lag several days behind that reported for MCP in mouse testis, suggesting the presence of selenium-free MCP in immature germ cells. SDS gel electrophoretic analysis of testis subcellular fractions 24 h after 75Se injection into rat testis at 21, 28 and 90 days of age indicates that sperm selenoprotein first appears in very low concentration during late meiosis and that its concentration increases sharply during early spermiogenesis. Additional 75Se-labelled polypeptides were detected on the gels, most of them of higher molecular weight than MCP. At least two of these (Mr 47,000 and 54,000) displayed a marked decrease in labelling between 5 and 24 h after injection into adult testis, coincident with a comparable increase in 75Se-labelled MCP, indicating that they may be precursors of MCP.     

Reproductive success,spontaneous embryo abortion,and genetic load in flowering plants

Summary Reproductive success is divided into two phases: preemergent (the number of viable seeds that enter the ambient environment) and postemergent (the percentage of progeny that survive to reproduce). We studied preemergent reproductive success (PERS) in flowering plants by measuring the fruit/flower (Fr/Fl) ratio and the seed/ovule (S/O) ratio in a number of species of outcrossing and inbreeding plants, where PERS=the product of (Fr/Fl) and (S/O). In order to determine the influence of the ambient environment (including resource availability) we studied pairs of outcrossing and inbreeding species occurring in the same habitat. Among outcrossing species PERS averaged about 22%, whereas in inbreeding species the average was approximately 90%. The progeny/zygote (P/Z) ratio was studied in hand-pollinated populations in Epilobium angustifolium (a strongly outcrossing species) from populations in Oregon and Utah, by direct observation of embryogenesis at twoday intervals throughout the course of seed development. The P/Z ratio in both populations averaged near 30%, and the developing embryos showed a surprising array of abnormalities that resulted in embryo death. During early development >95% of the ovules had normally developing globular embryos, but beginning with differentiation (cotyledon formation) about 70% of the original globular embryos aborted during the course of embryogenesis and seed development. The clustering of developmental lethals during peroids of major differentiation events parallels the animal model of development. We found little evidence that PERS was limited by the ambient environment (including resource availability), pollination, or factors associated with the inbreeding habit. Instead, PERS was found to be inextricably linked to outcrossing plants, whose breeding systems promote genetic variability. The high incidence of developmental lethals in E. angustifolium and the resulting low P/Z ratio (ca. 30%) is attributed to genetic load (any lethal mutation or allelic combination) possibly working in combination with developmental selection (interovarian competition among genetically diverse embryos). Examples of maternally controlled, fixed patterns of ovule abortion with respect to position or number are discussed. However, we found no need to employ female choice as a hypothesis to explain our results for the extensive, seemingly random patterns of embryo abortion in E. angustifolium and other outcrossing species. A more parsimonious, mechanistic explanation based on genetic load-developmental selection is sufficient to account for the differential survivorship of embryos. Likewise, the traditional concept of a positive growth regulator feedback system based on the number of surviving ovules in an ovary can account for subsequent fruit survivorship.     

The primary structure of the beta-subunit of the cell surface adhesion glycoproteins LFA-1, CR3 and p150,95 and its relationship to the fibronectin receptor.

The lymphocyte-function-associated antigen-1 (LFA-1), the complement receptor type 3 (CR3) and the antigen p150,95 are cell-surface glycoproteins. They are heterodimeric complexes, each containing a unique alpha-subunit noncovalently associated with a common beta-subunit. We have purified the beta-subunit from human spleen and obtained limited peptide sequences. What appears to be the complete primary structure for the fully processed beta-subunit was obtained by cDNA sequencing of clones from a phorbol ester (PMA) stimulated U937 cDNA library. There are five possible glycosylation sites and a transmembrane segment. The sequence contains a high level of cysteine (7.6%), with 24 of the 57 cysteine residues being found in three repeating units each with eight residues. The entire primary structure has 47% identity to a subunit of a fibronectin binding protein from chicken fibroblasts. It seems that LFA-1, CR3 and p150,95 antigens may belong to an extended family of cell surface molecules including the fibronectin binding protein.