       Document 0455
 DOCN  M9610455
 TI    Circular structures in retroviral and cellular genomes.
 DT    9601
 AU    Albert FG; Bronson EC; Fitzgerald DJ; Anderson JN; Department of
       Biological Sciences, Purdue University, West; Lafayette, Indiana 47907,
       USA.
 SO    J Biol Chem. 1995 Oct 6;270(40):23570-81. Unique Identifier : AIDSLINE
       GENBANK/M24197
 AB    A computer program for predicting DNA bending from nucleotide sequence
       was used to identify circular structures in retroviral and cellular
       genomes. An 830-base pair circular structure was located in a control
       region near the center of the genome of the human immunodeficiency virus
       type I (HIV-I). This unusual structure displayed relatively smooth
       planar bending throughout its length. The structure is conserved in
       diverse isolates of HIV-I, HIV-II, and simian immunodeficiency viruses,
       which implies that it is under selective constraints. A search of all
       sequences in the GenBank data base was carried out in order to identify
       similar circular structures in cellular DNA. The results revealed that
       the structures are associated with a wide range of sequences that
       undergo recombination, including most known examples of DNA inversion
       and subtelomeric translocation systems. Circular structures were also
       associated with replication and transposition systems where DNA looping
       has been implicated in the generation of large protein-DNA complexes.
       Experimental evidence for the structures was provided by studies which
       demonstrated that two sequences detected as circular by computer
       preferentially formed covalently closed circles during ligation
       reactions in vitro when compared to nonbent fragments, bent fragments
       with noncircular shapes, and total genomic DNA. In addition, a single
       T-->C substitution in one of these sequences rendered it less planar as
       seen by computer analysis and significantly reduced its rate of
       ligase-catalyzed cyclization. These results permit us to speculate that
       intrinsically circular structures facilitate DNA looping during
       formation of the large protein-DNA complexes that are involved in site-
       and region-specific recombination and in other genomic processes.
 DE    Animal  Caenorhabditis elegans/GENETICS  Databases, Factual  DNA,
       Circular/*CHEMISTRY/*GENETICS  DNA, Viral/*CHEMISTRY/*GENETICS  *Genome,
       Human  Human  HIV-1/GENETICS  HIV-2/GENETICS  Introns  Molecular
       Sequence Data  Molecular Structure  Nucleic Acid Conformation
       Recombination, Genetic  Retroviridae/*GENETICS  Software  Support, U.S.
       Gov't, P.H.S.  SIV/GENETICS  JOURNAL ARTICLE

       SOURCE: National Library of Medicine.  NOTICE: This material may be
       protected by Copyright Law (Title 17, U.S.Code).

