Fragment E1 Research Articles

Structure of fragment E species from human cross-linked fibrin.

Fragments E1, E2, and E3 are plasmic derivatives of fibrin encompassing the NH2-terminal region of the molecule. The first two species, but not the third, can bind to fragment DD, forming a (DD)E complex, and therefore probably contain binding sites involved in the polymerization of fibrin. For localization of these sites the structure of the fragments was determined by establishing the NH2- and COOH-terminal boundaries of the molecules and using the published amino acid sequence of fibrinogen. Fragment E1 encompasses Gly-alpha 17 to Lys-alpha 78, Gly-beta 15 to Lys-beta 122, and Tyr-gamma 1 to Lys-gamma 62, this representing the intact NH2-terminal region of fibrin. Fragment E2 is an asymmetric molecule which is lacking the sequence of Gly-beta 15 to Lys-beta 53 in one beta-chain remnant. This fragment E2 also lost Lys-beta 122 from the COOH terminal of the beta chain as compared with fragment E1. These cleavages did not affect the ability of fragment E2 to bind to fragment DD. Fragment E3 was heterogeneous, the main species encompassing Val-alpha 20 to Lys-alpha 78, Lys-beta 54 to Leu-beta 120, and Tyr-gamma 1 to Lys-gamma 53. Thus, the loss of the binding function involved in the formation of fibrin clot was associated with the removal of small fragments from all three polypeptide chains: alpha 17-19 (Gly-Pro-Arg), beta 15-53 from the remaining half of the molecule, beta 121 (Leu), and gamma 54-58 (Thr-Ser-Glu-Val-Lys).

Split gene for mitochondrial 24S ribosomal RNA of neurospora crassa

The 60 kb circular mitochondrial genome of N. crassa has previously been shown to contain a single transcription unit for 17S and 24S rRNA mapping within the largest Eco RI fragment E1 (19.6 kb). This fragment was isolated from uncloned mitochondrial DNA and further analyzed by cleavage with restriction endonucleases Hind II, Hind III, Bam HI, Pvu II and Bgl I, and by electron microscopy of rRNA/DNA hybrids. The resulting map shows a 2.3 kb intervening sequence interrupting the gene for 24S rRNA. The main part (2.7 kb) of this gene is separated from the 17S rRNA gene by a 5 kb segment which contains several transfer RNA genes. This segment is much longer than the putative 1 kb spacer sequence within the 32S precursor molecule for both rRNAs, suggesting a second splicing event in that region.

The Essential Covalent Structure of Human Fibrinogen Evinced by Analysis of Derivatives Formed during Plasmic Hydrolysis

Abstract In an effort to determine the essential structural features of human fibrinogen, plasmic hydrolysis was carried out and degradation products were identified and analyzed. In agreement with previous work, the initial attack was shown to occur in the Aα chains with the release of portions of their COOH-terminal regions (designated /α chains in the terminology developed to describe the present findings), whereas simultaneous, but slower, degradation occurs in the NH2-terminal region of the Bβ/ chains) and results in the removal of remnants (designated Bβ/ chains) containing peptide B. These changes, plus internal cleavages leading eventually to the separation of Fragments D and E (terminology of Nussenzweig et al.), produce a series of high molecular weight derivatives which can be separated by polyacrylamide gel electrophoresis of unreduced samples in sodium dodecyl sulfate. (These were designated Bands II through VII in order of decreasing molecular size; Band VII was identified as Fragment X in the terminology of Marder et al.) Upon further hydrolysis derivative Band VII can lose the COOH-terminal portion of one of its Bβ chains (as remnant /β6, molecular weight 32,000) to form derivative Band VIII (Fragment Y in the terminology of Marder et al.) or, alternatively, can undergo cleavage to yield early forms of Fragments D and E (designated D1 and E1, respectively). Derivative Band VIII, in turn, is degraded to Fragment E1 plus a later form of Fragment D. Once cleaved from the parent molecule, these Fragments D continue to release /β chains. These degradative pathways lead to a series of Fragments D (D1 through D5) which differ in molecular weight. Additional cleavages occur in Fragment E1 to form a smaller fragment (E2) which, unlike E1, lacks peptide A. Immunochemical studies of derivatives obtained at successive phases of digestion demonstrated the presence of at least five antigenic determinants on the fibrinogen molecule. One of these is located on /α chains; another, on Fragment E; three others, on Fragment D. Of the latter, one is associated with /β6 chains; a second (designated F) is associated with Fragments F, which arise by further degradation of Fragments D; the third (designated D) is that lost when Fragment F is evolved. Electrophoretic behavior of plasmic derivatives before and after reduction revealed at least one intrachain disulfide bridge in each /α15 and /β6 chain. Studies of Fragment D subunit composition and recovery at various phases of digestion indicated that it is a dimeric structure containing substantial portions of the COOH-terminal region of both γ chains (as /γ1 remnant chains, each having a molecular weight of 42,000) and hence that only one such fragment (linked by at least five interchain disulfide bridges) can be generated by each fibrinogen molecule. These results, plus those reported by others, led to the conclusion that fibrinogen itself has a dimeric structure, the backbone of which consists of a pair of γ chains linked directly to each other by disulfide bridging in the NH2-terminal region and covalently linked (enter directly or indirectly) with the Aα and Bβ chains in at least two regions of the molecule.