title: The structure of Sinorhizobium meliloti phage ΦM12, which has a novel T=19l triangulation number and is the founder of a new group of T4-superfamily phages.
abstract: ΦM12 is the first example of a T=19l geometry capsid, encapsulating the recently sequenced genome. Here, we present structures determined by cryo-EM of full and empty capsids. The structure reveals the pattern for assembly of 1140 HK97-like capsid proteins, pointing to interactions at the pseudo 3-fold symmetry axes that hold together the asymmetric unit. The particular smooth surface of the capsid, along with a lack of accessory coat proteins encoded by the genome, suggest that this interface is the primary mechanism for capsid assembly. Two-dimensional averages of the tail, including the neck and baseplate, reveal that ΦM12 has a relatively narrow neck that attaches the tail to the capsid, as well as a three-layer baseplate. When free from DNA, the icosahedral edges expand by about 5nm, while the vertices stay at the same position, forming a similarly smooth, but bowed, T=19l icosahedral capsid.
authors: Department of Biological Science, Florida State University, Biology Unit I, 230A, 91 Chieftan Way, Tallahassee, FL, 32306-4370, United States; Institute of Molecular Biophysics, Florida State University, 91 Chieftan Way, Tallahassee, FL, 32306-4370, United States. Electronic address: mestroupe@bio.fsu.edu.
authors: M Elizabeth
authors: ME
authors: Stroupe
authors: Department of Biological Science, Florida State University, Biology Unit I, 230A, 91 Chieftan Way, Tallahassee, FL, 32306-4370, United States.
authors: Tess E
authors: TE
authors: Brewer
authors: Department of Biological Science, Florida State University, Biology Unit I, 230A, 91 Chieftan Way, Tallahassee, FL, 32306-4370, United States; Institute of Molecular Biophysics, Florida State University, 91 Chieftan Way, Tallahassee, FL, 32306-4370, United States.
authors: Duncan R
authors: DR
authors: Sousa
authors: Department of Biological Science, Florida State University, Biology Unit I, 230A, 91 Chieftan Way, Tallahassee, FL, 32306-4370, United States.
authors: Kathryn M
authors: KM
authors: Jones
mesh_terms: D000595:Amino Acid Sequence; D017122:Bacteriophage T4 / Q000235:genetics / Q000302:isolation & purification* / Q000648:ultrastructure*; D002213:Capsid / Q000378:metabolism / Q000648:ultrastructure*; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics; D020285:Cryoelectron Microscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D016962:Sinorhizobium meliloti / Q000821:virology*
chemical_list: D036022:Capsid Proteins
keywords: Bacteriophage; Icosahedral; Myovirus; Sinorhizobium meliloti; T=19; ΦM12