title: Genetics of critical contacts and clashes in the DNA packaging specificities of bacteriophages λ and 21.
abstract: The cos sites in λ and 21 chromosomes contain binding sites that recruit terminase to initiate DNA packaging. The small subunits of terminase, gpNu1 (λ) and gp1 (21), have winged helix-turn-helix DNA binding domains, where the recognition helixes differ in four of nine residues. To initiate packaging, the small subunit binds three R sequences in the cosB subsite. λ and 21 cannot package each other׳s DNA, due to recognition helix and R sequence differences. In λ and 21 cosBs, two bp, tri1 and tri2, are conserved in the R sequences yet differ between the phages; they are proposed to play a role in phage-specific packaging by λ and 21. Genetic experiments done with mixed and matched terminase and cosB alleles show packaging specificity depends on favorable contacts and clashes. These interactions indicate that the recognition helixes orient with residues 20 and 24 proximal to tri2 and tri1, respectively.
authors.affiliation: Department of Microbiology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 51 Newton Road, Iowa City, IA 52242, United States. Electronic address: jean-sippy@uiowa.edu.
authors.forename: Jean
authors.initials: J
authors.lastname: Sippy
authors.affiliation: University Hospitals and Clinics (UIHC), Department of Pathology, 200 Hawkins Dr. 6240 RCP, Iowa City, IA 52242, United States. Electronic address: priyal-patel@uiowa.edu.
authors.forename: Priyal
authors.initials: P
authors.lastname: Patel
authors.affiliation: Department of Microbiology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 51 Newton Road, Iowa City, IA 52242, United States. Electronic address: vahanian.nicole@gmail.com.
authors.forename: Nicole
authors.initials: N
authors.lastname: Vahanian
authors.affiliation: Department of Population Health Sciences, University of Wisconsin-Madison, 610 North Walnut Street, Madison, WI 53726, United States. Electronic address: sippy@wisc.edu.
authors.forename: Rachel
authors.initials: R
authors.lastname: Sippy
authors.affiliation: Department of Microbiology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 51 Newton Road, Iowa City, IA 52242, United States. Electronic address: michael-feiss@uiowa.edu.
authors.forename: Michael
authors.initials: M
authors.lastname: Feiss
mesh_terms: D000595:Amino Acid Sequence; D001435:Bacteriophages / Q000737:chemistry / Q000201:enzymology / Q000235:genetics* / Q000502:physiology; D001665:Binding Sites; D042003:DNA Packaging; D004279:DNA, Viral / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016415:Sequence Alignment; D013045:Species Specificity; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D004279:DNA, Viral; D014764:Viral Proteins; D004706:Endodeoxyribonucleases; C030894:terminase
keywords: DNA recognition; TerS; Terminase; Viral packaging; Virus assembly