P
rotein p6 f
rom
Bacillus subtilis phage &
Oslash;29(
Mr = 11 800) binds
in vitro toDNA fo
rming ala
rge nucleop
rotein complex in which the DNA w
raps a multime
ric p
roteinco
re. The high int
racellula
rabundance of p
rotein p6 togethe
r with its ability to bind the wholeØ29 DNA
in vitro st
rongly suggeststhat it plays a
role in vi
ral genome o
rganization. We havedete
rmined by sedimentation equilib
riumanalysis that p
rotein p6 (1-100
![](/images/entities/mg<font color=)
r.gif">M
range), in the absence of DNA,is in a monome
r-dime
r equilib
rium,with an association constant (
K2) of ~2 ×10
5 M
-1. The int
racellula
rconcent
ration of p
rotein p6 (~1mM) was estimated measu
ring the numbe
r of copies pe
r cell (7 ×10
5) and the cell volume (1 ×10
-15L). At concent
rations a
round 1 mM, p
rotein p6 associates intooligome
rs. This self-association behavio
ris compatible with a dime
r-hexame
r model (
K2,6= 3.2 × 10
8 M
-2) o
r with anisodesmic association ofthe dime
r (
K = 950 M
-1), becausethe appa
rent weight-ave
rage molecula
r mass(
Mw,a) does not
reachsatu
ration at the highest p
rotein concent
rations. Thesedimentation coefficients of p
rotein p6 monome
rand dime
r we
re 1.4 and 2.0,
respectively, compatible with t
ranslationalf
rictional
ratios (
f/
fo) of 1.15and1.30, which slightly deviate f
rom the hyd
rodynamics of a
rigid globula
rp
rotein. Ta
king togethe
r these
results and conside
ring the st
ructu
re of the nucleop
rotein complex, wespeculate that the obse
rved oligome
rsof p
rotein p6 could mimic a scaffold on which DNA folds to fo
rm thenucleop
rotein complex
in vivo.