Barrier-to-autointegration factor (breakpoint cluster region protein 1, BANF1, BAF, BCRG1)
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Function
- roles in nuclear assembly, chromatin organization, gene expression & gonad development
- may compress chromatin structure & be involved in membrane recruitment & chromatin decondensation during nuclear assembly
- contains 2 nonspecific dsDNA-binding sites which may promote DNA cross-bridging.
- homodimer, heterodimerizes with BAFL
- binds non nonspecifically to double-stranded DNA, & is found as a hexamer or dodecamer upon DNA binding
- binds to LEM domain-containing nuclear proteins including LEMD3/MAN1, TMPO/LAP2 & EMD (emerin)
- interacts with CRX & LMNA (lamin-A)
- binds linker histone H1.1 & core histones H3 with in vitro affinities of 500-900 & 100-200 nM.
- partially phosphorylated on serine
- Ser-4 phosphorylation may block BAF ability to promote EMD binding to lamins in vitro.
- non phosphorylated BAF seems to enhances binding between EMD & LMNA
Structure
- belongs to the BAF family
- has a helix-hairpin-helix (HhH) structural motif conserved among proteins that bind nonspecifically to DNA
- LEM domain proteins bind centrally on the BAF dimer, DNA binds to the left & right sides
Compartment
- nucleus, cytoplasm
- significantly enriched at the nuclear inner membrane, diffusely throughout nucleus during interphase & concentrated at the chromosomes during M-phase
Expression
- widely expressed
- expressed in colon, brain, heart, kidney, liver, lung, ovary, pancreas, placenta, prostate, skeletal muscle, small intestine, spleen, testis
- not detected in thymus & peripheral blood leukocytes
Pathology
- exploited by retroviruses for inhibiting self-destructing autointegration of retroviral DNA, thereby promoting integration of viral DNA into the host chromosome
- interacts with HIV-1 pre-integration complex in cytoplasm by binding to viral matrix protein & GAG polyprotei
- may be included in HIV-1 virions via its interaction with viral GAG polyprotein