ISSN:0021-9541    

DOI:10.1002/jcp.1040740423

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

ISSN:0021-9541    

DOI:10.1002/jcp.1040740424

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

ISSN:0021-9541    

DOI:10.1002/jcp.1040740425

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

ISSN:0021-9541    

DOI:10.1002/jcp.1040740426

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

摘要:

AbstractAssemblies of protein molecules represent a fundamental level of biological organization. The dynamic behavior of these systems–including both the assembly process and functional rearrangements–may be accounted for by the specificity of the protein interactions, which depend on environmental conditions. Analysis of the self‐assembly of virus particles has established that the design of an ordered structure can be built into the specific bonding properties of the constituent proteins. Any structure which can change its state of organization is, by definition, polymorphic. The distinctive aspect of polymorphism in protein structures, contrasted with nonliving states of matter, is that the molecular design has been selected to carry out a function and that this function is part of an integrated system. The differences in molecular conformation and arrangement in all polymorphic structures–for example, allosteric enzymes or ice crystals–depend on the intrinsic interaction properties of the molecules themselves. The structures of ice and water illustrate relations between specificity and polymorphism which are relevant to the form and function of protein assemblies.Two types of polymorphism can be distinguished: modal polymorphism, which is externally moderated, as in phase transitions between different crystals forms; and positional polymorphism, which is internally moderated, as in the different disposition of identical molecules within a single crystal lattice. Positional polymorphism, exemplified by the quasi‐equivalent bonding of icosahedral virus coat proteins and the different arrangement of myosin and paramyosin at the center and polar portions of the bipolar filaments, results from specific interactions that are not compatible with a strictly equivalent packing of identical molecules. The structural rearrangements in muscle contraction and the switching between the oxy and deoxy forms of hemoglobin represent the formation of different structures in response to altered external conditions. The different structural states of many protein assemblies are characterized by conserved connections which may be regarded as providing the framework for functional rearrangements. The types of polymorphism displayed by hemoglobin, virus, and muscle proteins demonstrate the relevance of the simple view that the function of a protein is determined by the potential structures

ISSN:0021-9541    

DOI:10.1002/jcp.1040740427

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

摘要:

AbstractFunctionally active 30S ribosomes can be reconstitutedin vitrofrom 16S RNA and a mixture of 30S ribosomal proteins under certain defined conditions. Our previous studies on the specificity and kinetics of reconstitution are summarized and discussed. The reconstitution reaction is first‐order with respect to formation of active 30S ribosomes. The rate‐limiting reaction is probably unimolecular, and it represents the structural rearrangement of an intermediate. Presumed reconstitution intermediates, or RI particles, have been isolated from reconstitution mixtures incubated at low temperature. It has been concluded that the reconstitution takes place in stepwise fashion: 16S ribosomes. New experimental results that show the highly cooperative nature of the assembly reaction are described; the number of sites, per RNA chain, which can bind ribosomal proteins independently from each other (i.e., without cooperativity) is at most two to three. Finally, another approach to the study of ribosome assemblyin vivois described. It utilizes cold‐sensitiveE. colimutants that are defective in ribosome biosynthesis at low temperature and accumulate incomplete “intermediate” ribosomal

ISSN:0021-9541    

DOI:10.1002/jcp.1040740428

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

ISSN:0021-9541    

DOI:10.1002/jcp.1040740429

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

ISSN:0021-9541    

DOI:10.1002/jcp.1040740402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY