Homology of 54K protein of signal-recognition particle, docking protein and two E. coli proteins with putative GTP–binding domains

MOST proteins exported from mammalian cells contain a signal sequence which mediates targeting to and insertion into the mem-brane of the endoplasmic reticulum (ER)1,2. Involved in this process are the signal-recognition particle (SRP) and docking protein (DP), the receptor for SRP in the ER membrane1. SRP interacts with the signal sequence on nascent polypeptide chains and retards their further elongation1, which resumes only after interaction of the arrested ribosomal complex with the docking protein3,4. SRP is a ribonucleoprotein particle comprising a 7S RNA and six polypeptides with relative molecular masses (Mr) of 9,000 (9K) 14K, 19K, 54K, 68K and 72K (ref. 1). The 9K and 14K proteins are essential for elongation arrest and the 68K–72K heterodimer is required for docking to the ER membrane5. The 54K protein binds to the signal sequence when it emerges from the ribosome6,7. Docking protein consists of two polypeptides, a 72K α-summit (DPα) and a 30K β-subunit (DPβ)8. No components structurally homologous to SRP and docking protein have yet been found in yeast or Escherichia coli. To understand the molecular nature of the interaction between the signal sequence and its receptor(s) we have characterized a complementary DNA coding for the 54K protein of SRP. Significant sequence homology was found to part of DPα and two E. coli proteins of unknown function. The homologous region includes a putative GTP–binding domain.

[1]  G. Church,et al.  Genomic sequencing. , 1993, Methods in molecular biology.

[2]  D. Lipman,et al.  Improved tools for biological sequence comparison. , 1988, Proceedings of the National Academy of Sciences of the United States of America.

[3]  A. Byström,et al.  The nucleotide sequence of an Escherichia coli operon containing genes for the tRNA(m1G)methyltransferase, the ribosomal proteins S16 and L19 and a 21‐K polypeptide. , 1983, The EMBO journal.

[4]  P. Walter,et al.  Each of the activities of signal recognition particle (SRP) is contained within a distinct domain: Analysis of biochemical mutants of SRP , 1988, Cell.

[5]  P. Walter,et al.  Photocrosslinking of the signal sequence of nascent preprolactin to the 54-kilodalton polypeptide of the signal recognition particle. , 1986, Proceedings of the National Academy of Sciences of the United States of America.

[6]  A. Kleinzeller,et al.  Current Topics in Membranes and Transport , 1970 .

[7]  V. L. Rath,et al.  The signal recognition particle receptor is a complex that contains two distinct polypeptide chains , 1986, The Journal of cell biology.

[8]  L. Randall,et al.  Export of protein: a biochemical view. , 1987, Annual review of microbiology.

[9]  A. Ullrich,et al.  Topology of signal recognition particle receptor in endoplasmic reticulum membrane , 1985, Nature.

[10]  H. Bourne.  Do GTPases direct membrane traffic in secretion? , 1988, Cell.

[11]  B. Dobberstein,et al.  Secretory protein translocation across membranes—the role of the ‘docking protein’ , 1982, Nature.

[12]  C. Zwieb,et al.  Isolation and characterization of a cDNA clone encoding the 19 kDa protein of signal recognition particle (SRP): expression and binding to 7SL RNA. , 1988, Nucleic acids research.

[13]  B. Clark,et al.  Structural details of the binding of guanosine diphosphate to elongation factor Tu from E. coli as studied by X‐ray crystallography. , 1985, The EMBO journal.

[14]  J. Herz,et al.  Efficient construction of cDNA libraries in plasmid expression vectors using an adaptor strategy. , 1986, Nucleic acids research.

[15]  H. Pelham,et al.  Involvement of ATP in the nuclear and nucleolar functions of the 70 kd heat shock protein. , 1985, The EMBO journal.

[16]  G. Blobel,et al.  Disassembly and reconstitution of signal recognition particle , 1983, Cell.

[17]  W. Ansorge.  Fast and sensitive detection of protein and DNA bands by treatment with potassium permanganate. , 1985, Journal of biochemical and biophysical methods.

[18]  T. Connolly,et al.  The signal recognition particle receptor mediates the GTP-dependent displacement of SRP from the signal sequence of the nascent polypeptide , 1989, Cell.

[19]  B. Dobberstein,et al.  Disassembly and domain structure of the proteins in the signal-recognition particle. , 1987, European journal of biochemistry.

[20]  M Lanzer,et al.  A T5 promoter-based transcription-translation system for the analysis of proteins in vitro and in vivo. , 1987, Methods in enzymology.

[21]  T. Rapoport,et al.  Direct probing of the interaction between the signal sequence of nascent preprolactin and the signal recognition particle by specific cross-linking , 1987, The Journal of cell biology.

[22]  S H Kim,et al.  Three-dimensional structure of an oncogene protein: catalytic domain of human c-H-ras p21. , 1988, Science.

[23]  L. Randall,et al.  Unity in function in the absence of consensus in sequence: role of leader peptides in export. , 1989, Science.

[24]  P. Walter,et al.  Mechanism of protein translocation across the endoplasmic reticulum membrane. , 1986, Annual review of cell biology.

[25]  M. Kozak.  The scanning model for translation: an update , 1989, The Journal of cell biology.