TY - JOUR
T1 - Investigation of stoichiometry of T4 bacteriophage helicase loader protein (gp59)
AU - Arumugam, Sri Ranjini
AU - Lee, Tae Hee
AU - Benkovic, Stephen J.
PY - 2009/10/23
Y1 - 2009/10/23
N2 - The T4 bacteriophage helicase loader (gp59) is one of the main eight proteins that play an active role in the replisome. gp59 is a small protein (26 kDa) that exists as a monomer in solution and in the crystal. It binds preferentially to forked DNA and interacts directly with the T4 helicase (gp41), single-stranded DNA-binding protein (gp32), and polymerase (gp43). However, the stoichiometry and structure of the functional form are not very well understood. There is experimental evidence for a hexameric structure for the helicase (gp41) and the primase (gp61), inferring that the gp59 structure might also be hexameric. Various experimental approaches, including gel shift, fluorescence anisotropy, light scattering, and fluorescence correlation spectroscopy, have not provided a clearer understanding of the stoichiometry. In this study, we employed single-molecule photobleaching (smPB) experiments to elucidate the stoichiometry of gp59 on a forked DNA and to investigate its interaction with other proteins forming the primosome complex. smPB studies were performed with Alexa 555-labeled gp59 proteins and a forked DNA substrate. Co-localization experiments were performed using Cy5-labeled forked DNA and Alexa 555-labeled gp59 in the presence and absence of gp32 and gp41 proteins. A systematic study of smPB experiments and subsequent data analysis using a simple model indicated that gp59 on the forked DNA forms a hexamer. In addition, the presence of gp32 and gp41 proteins increases the stability of the gp59 complex, emphasizing their functional role in T4 DNA replication machinery.
AB - The T4 bacteriophage helicase loader (gp59) is one of the main eight proteins that play an active role in the replisome. gp59 is a small protein (26 kDa) that exists as a monomer in solution and in the crystal. It binds preferentially to forked DNA and interacts directly with the T4 helicase (gp41), single-stranded DNA-binding protein (gp32), and polymerase (gp43). However, the stoichiometry and structure of the functional form are not very well understood. There is experimental evidence for a hexameric structure for the helicase (gp41) and the primase (gp61), inferring that the gp59 structure might also be hexameric. Various experimental approaches, including gel shift, fluorescence anisotropy, light scattering, and fluorescence correlation spectroscopy, have not provided a clearer understanding of the stoichiometry. In this study, we employed single-molecule photobleaching (smPB) experiments to elucidate the stoichiometry of gp59 on a forked DNA and to investigate its interaction with other proteins forming the primosome complex. smPB studies were performed with Alexa 555-labeled gp59 proteins and a forked DNA substrate. Co-localization experiments were performed using Cy5-labeled forked DNA and Alexa 555-labeled gp59 in the presence and absence of gp32 and gp41 proteins. A systematic study of smPB experiments and subsequent data analysis using a simple model indicated that gp59 on the forked DNA forms a hexamer. In addition, the presence of gp32 and gp41 proteins increases the stability of the gp59 complex, emphasizing their functional role in T4 DNA replication machinery.
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U2 - 10.1074/jbc.M109.029926
DO - 10.1074/jbc.M109.029926
M3 - Article
C2 - 19700405
AN - SCOPUS:70350350044
SN - 0021-9258
VL - 284
SP - 29283
EP - 29289
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 43
ER -