The Structure of the Phage T4 DNA Packaging Motor Suggests a Mechanism Dependent on Electrostatic Forces

SummaryViral genomes are packaged into “procapsids” by powerful molecular motors. We report the crystal structure of the DNA packaging motor protein, gene product 17 (gp17), in bacteriophage T4. The structure consists of an N-terminal ATPase domain, which provides energy for compacting DNA, and a C-terminal nuclease domain, which terminates packaging. We show that another function of the C-terminal domain is to translocate the genome into the procapsid. The two domains are in close contact in the crystal structure, representing a “tensed state.” A cryo-electron microscopy reconstruction of the T4 procapsid complexed with gp17 shows that the packaging motor is a pentamer and that the domains within each monomer are spatially separated, representing a “relaxed state.” These structures suggest a mechanism, supported by mutational and other data, in which electrostatic forces drive the DNA packaging by alternating between tensed and relaxed states. Similar mechanisms may occur in other molecular motors

Regulation by interdomain communication of a headful packaging nuclease from bacteriophage T4

In genome packaging by tailed bacteriophages and herpesviruses, a concatemeric DNA is cut and inserted into an empty procapsid. A series of cuts follow the encapsidation of each unit-length ‘headful’ genome, but the mechanisms by which cutting is coupled to packaging are not understood. Here we report the first biochemical characterization of a headful nuclease from bacteriophage T4. Our results show that the T4 nuclease, which resides in the C-terminal domain of large ‘terminase’ gp17, is a weak endonuclease and regulated by a variety of factors; Mg, NaCl, ATP, small terminase gp16 and N-terminal ATPase domain. The small terminase, which stimulates gp17-ATPase, also stimulates nuclease in the presence of ATP but inhibits in the absence of ATP suggesting interdomain crosstalk. Comparison of the ‘relaxed’ and ‘tensed’ states of the motor show that a number of basic residues lining the nuclease groove are positioned to interact with DNA in the tensed state but change their positions in the relaxed state. These results suggest that conformational changes in the ATPase center remodel the nuclease center via an interdomain ‘communication track’. This might be a common regulatory mechanism for coupling DNA cutting to DNA packaging among the headful packaging nucleases from dsDNA viruses

Australia\u27s health 2002 : the eighth biennial report of the Australian Institute of Health and Welfare

Australia\u27s Health 2002 is the eighth biennial health report of the Australian Institute of Health and Welfare. It is the nation\u27s authoritative source of information on patterns of health and illness, determinants of health, the supply and use of health services, and health service costs and performance. Australia\u27s Health 2002 is an essential reference and information resource for all Australians with an interest in health

Social learning among Congo Basin hunter–gatherers

This paper explores childhood social learning among Aka and Bofi hunter–gatherers in Central Africa. Existing literature suggests that hunter–gatherer social learning is primarily vertical (parent-to-child) and that teaching is rare. We use behavioural observations, open-ended and semi-structured interviews, and informal and anecdotal observations to examine the modes (e.g. vertical versus horizontal/oblique) and processes (e.g. teaching versus observation and imitation) of cultural transmission. Cultural and demographic contexts of social learning associated with the modes and processes of cultural transmission are described. Hunter–gatherer social learning occurred early, was relatively rapid, primarily vertical under age 5 and oblique and horizontal between the ages of 6 and 12. Pedagogy and other forms of teaching existed as early as 12 months of age, but were relatively infrequent by comparison to other processes of social learning such as observation and imitation