ID   M1_INBYA                Reviewed;         248 AA.
AC   Q71UK7;
DT   10-JAN-2006, integrated into UniProtKB/Swiss-Prot.
DT   05-JUL-2004, sequence version 1.
DT   29-SEP-2021, entry version 70.
DE   RecName: Full=Matrix protein 1 {ECO:0000255|HAMAP-Rule:MF_04068};
DE            Short=M1 {ECO:0000255|HAMAP-Rule:MF_04068};
GN   Name=M {ECO:0000255|HAMAP-Rule:MF_04068};
OS   Influenza B virus (strain B/Yamagata/1/1973).
OC   Viruses; Riboviria; Orthornavirae; Negarnaviricota; Polyploviricotina;
OC   Insthoviricetes; Articulavirales; Orthomyxoviridae; Betainfluenzavirus.
OX   NCBI_TaxID=11550;
OH   NCBI_TaxID=9606; Homo sapiens (Human).
RN   [1]
RP   NUCLEOTIDE SEQUENCE [GENOMIC RNA].
RX   PubMed=10573149; DOI=10.1099/0022-1317-80-10-2573;
RA   Odagiri T., Hong J., Ohara Y.;
RT   "The BM2 protein of influenza B virus is synthesized in the late phase of
RT   infection and incorporated into virions as a subviral component.";
RL   J. Gen. Virol. 80:2573-2581(1999).
CC   -!- FUNCTION: Plays critical roles in virus replication, from virus entry
CC       and uncoating to assembly and budding of the virus particle. M1 binding
CC       to ribonucleocapsids (RNPs) in nucleus seems to inhibit viral
CC       transcription. Interaction of viral NEP with M1-RNP is thought to
CC       promote nuclear export of the complex, which is targeted to the virion
CC       assembly site at the apical plasma membrane in polarized epithelial
CC       cells. Interactions with NA and HA may bring M1, a non-raft-associated
CC       protein, into lipid rafts. Forms a continuous shell on the inner side
CC       of the lipid bilayer in virion, where it binds the RNP. During virus
CC       entry into cell, the M2 ion channel acidifies the internal virion core,
CC       inducing M1 dissociation from the RNP. M1-free RNPs are transported to
CC       the nucleus, where viral transcription and replication can take place.
CC       {ECO:0000255|HAMAP-Rule:MF_04068}.
CC   -!- FUNCTION: Determines the virion's shape: spherical or filamentous.
CC       Clinical isolates of influenza are characterized by the presence of
CC       significant proportion of filamentous virions, whereas after multiple
CC       passage on eggs or cell culture, virions have only spherical
CC       morphology. Filamentous virions are thought to be important to infect
CC       neighboring cells, and spherical virions more suited to spread through
CC       aerosol between hosts organisms. {ECO:0000255|HAMAP-Rule:MF_04068}.
CC   -!- SUBUNIT: Homodimer and homomultimer. Interacts with NEP. Binds
CC       ribonucleocapsid by both interacting with genomic RNA and NP protein.
CC       May interact with HA and NA. Cannot bind NP without genomic RNA.
CC       {ECO:0000255|HAMAP-Rule:MF_04068}.
CC   -!- SUBCELLULAR LOCATION: Virion membrane {ECO:0000255|HAMAP-
CC       Rule:MF_04068}; Peripheral membrane protein {ECO:0000255|HAMAP-
CC       Rule:MF_04068}; Cytoplasmic side {ECO:0000255|HAMAP-Rule:MF_04068}.
CC       Host nucleus {ECO:0000255|HAMAP-Rule:MF_04068}.
CC   -!- MISCELLANEOUS: Influenza B virus genome RNA segment 7 encodes the M1
CC       and BM2 (AC P0C0X4) proteins. Normal translation produces the M1
CC       protein. The M1 termination codon overlaps the BM2 initiation codon in
CC       an overlapping stop-start pentanucleotide 5'-UAAUG-3'. Termination of
CC       M1 translation triggers reinitiation on the BM2 AUG in the +2 open
CC       reading frame.
CC   -!- MISCELLANEOUS: Most abundant protein in virion. When expressed alone
CC       can form virus-like particles in transfected cells. {ECO:0000255|HAMAP-
CC       Rule:MF_04068}.
CC   -!- SIMILARITY: Belongs to the influenza viruses Matrix protein M1 family.
CC       {ECO:0000255|HAMAP-Rule:MF_04068}.
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DR   EMBL; AF077348; AAD47140.1; -; Genomic_RNA.
DR   SMR; Q71UK7; -.
DR   GO; GO:0042025; C:host cell nucleus; IEA:UniProtKB-SubCell.
DR   GO; GO:0016020; C:membrane; IEA:UniProtKB-KW.
DR   GO; GO:0055036; C:virion membrane; IEA:UniProtKB-SubCell.
DR   GO; GO:0003723; F:RNA binding; IEA:UniProtKB-UniRule.
DR   GO; GO:0039660; F:structural constituent of virion; IEA:UniProtKB-UniRule.
DR   GO; GO:0046761; P:viral budding from plasma membrane; IEA:UniProtKB-UniRule.
DR   Gene3D; 1.10.10.180; -; 1.
DR   Gene3D; 1.20.91.10; -; 1.
DR   HAMAP; MF_04068; INFV_M1; 1.
DR   InterPro; IPR036039; Flu_matrix_M1.
DR   InterPro; IPR013188; Flu_matrix_M1_C.
DR   InterPro; IPR001561; Flu_matrix_M1_N.
DR   InterPro; IPR015423; Flu_matrix_M1_N_sub1.
DR   InterPro; IPR015799; Flu_matrix_M1_N_sub2.
DR   InterPro; IPR037533; INFV_M1.
DR   Pfam; PF00598; Flu_M1; 1.
DR   Pfam; PF08289; Flu_M1_C; 1.
DR   SMART; SM00759; Flu_M1_C; 1.
DR   SUPFAM; SSF48145; SSF48145; 1.
PE   3: Inferred from homology;
KW   Host nucleus; Membrane; RNA-binding; Viral matrix protein; Virion.
FT   CHAIN           1..248
FT                   /note="Matrix protein 1"
FT                   /id="PRO_0000078875"
FT   REGION          1..164
FT                   /note="Membrane-binding"
FT                   /evidence="ECO:0000255|HAMAP-Rule:MF_04068"
FT   REGION          165..248
FT                   /note="RNP-binding"
FT                   /evidence="ECO:0000255|HAMAP-Rule:MF_04068"
FT   MOTIF           101..105
FT                   /note="Nuclear localization signal"
FT                   /evidence="ECO:0000255|HAMAP-Rule:MF_04068"
SQ   SEQUENCE   248 AA;  27415 MW;  714F22C7319711C3 CRC64;
     MSLFGDTIAY LLSLTEDGEG KAELAEKLHC WFGGKEFDLD SALEWIKNKR CLTDIQKALI
     GASICFLKPK DQERKRRFIT EPLSGMGTTA TKKKGLILAE RKMRRCVSFH EAFEIAEGHE
     SSALLYCLMV MYLNPGNYSM QVKLGTLCAL CEKQASHSHR AHSRAARSSV PGVRREMQMV
     SAMNTAKTMN GMGKGEDVQK LAEELQSNIG VLRSLGASQK NGEGIAKDVM EVLKQSSMGN
     SALVKKYL