RESUMO
A range of related nucleic acid models has been built using the computer graphics system at EMBL (Heidelberg). The relationship between these models is considered in terms of a simple "core" structure. One of these models is a four-strand structure in which two duplexes of the Watson-Crick kind are specifically related by a twofold rotation axis and which has already been discussed in some detail. The models fall into two principal classes. In one, each sugar phosphate chain is attached to every layer of bases in the "core" structure; in the other, each chain is attached to alternate layers of bases. Several of the models discussed have specificity both of complementarity and of identity.
Assuntos
Gráficos por Computador , DNA/química , Modelos Moleculares , FotografaçãoRESUMO
Silk-moth chorion proteins belong to a small number of families: A, B, C, Hc-A and Hc-B. The central domain is an evolutionarily conservative region in each family, of variable length and composition between families. This domain shows clear 6-fold periodicities for various amino acid residues, e.g. glycine. The periodicities, together with the well-documented prevalence of beta-sheet and beta-turn secondary structure of chorion proteins, strongly support a structural model in which four-residue beta-strands alternate with beta-turns, forming a compact antiparallel, probably twisted beta-sheet. Conformational analysis, aided by interactive graphics refinement and recent experimental findings, further suggest that this structure consists of beta-strands, alternating with I' and II' beta-turns, and apparently forms the basis for the molecular and supramolecular assembly of chorion.
Assuntos
Proteínas do Ovo , Sequência de Aminoácidos , Animais , Proteínas de Membrana , Modelos Moleculares , Dados de Sequência Molecular , Conformação ProteicaRESUMO
A single-helical B-type geometry is presented based on 1H NMR observations on d(TATA) and several other small single-helical DNA fragments. The structure is extended to one complete turn of double-helical DNA and its characteristics are compared with other known B-type structures.
