TI  - Interactions among members of the <prot>Bcl-2</prot> protein family analyzed with a
      yeast two-hybrid system.
PG  - 9238-42
AB  - Interactions of the       <prot>Bcl-2</prot>       protein with itself and other members of the
      <prot>Bcl-2</prot> family, including  <prot>Bcl-X-L</prot> ,  <prot>Bcl-X-S</prot> ,  <prot>Mcl-1</prot> , and  <prot>Bax</prot> , were explored
      with a yeast two-hybrid system. Fusion proteins were created by linking
      <prot>Bcl-2</prot> family proteins to a LexA DNA-binding domain or a B42
      trans-activation domain. Protein-protein interactions were examined by
      expression of these fusion proteins in Saccharomyces cerevisiae having a
      lacZ (beta-galactosidase) gene under control of a LexA-dependent operator.
      This approach gave evidence for   <prot>Bcl-2</prot> protein   homodimerization.     <prot>Bcl-2</prot>     also
      interacted with  <prot>Bcl-X-L</prot>  and  <prot>Mcl-1</prot>  and with the dominant inhibitors  <prot>Bax</prot>  and
       <prot>Bcl-X-S</prot> .  <prot>Bcl-X-L</prot>  displayed the same pattern of combinatorial interactions
      with  <prot>Bcl-2</prot>  family proteins as <prot>Bcl-2</prot>. Use of deletion mutants of <prot>Bcl-2</prot>
      suggested that   <prot>Bcl-2</prot>   homodimerization involves interactions between two
      distinct regions within the <prot>Bcl-2</prot> protein, since a LexA protein containing
      <prot>Bcl-2</prot> amino acids 83-218 mediated functional interactions with a B42
      fusion protein containing <prot>Bcl-2</prot> amino acids 1-81 but did not complement a
      B42 fusion protein containing <prot>Bcl-2</prot> amino acids 83-218. In contrast to
      LexA/<prot>Bcl-2</prot> fusion proteins, expression of a LexA/<prot>Bax</prot> protein was lethal to
      yeast. This cytotoxicity could be abrogated by B42 fusion proteins
      containing <prot>Bcl-2</prot>, <prot>Bcl-X-L</prot>, or <prot>Mcl-1</prot> but not those containing <prot>Bcl-X-S</prot> (an
      alternatively spliced form of <prot>Bcl-X</prot> that lacks a well-conserved 63-amino
      acid region). The findings suggest a model whereby <prot>Bax</prot> and <prot>Bcl-X-S</prot>
      differentially regulate <prot>Bcl-2</prot> function, and indicate that requirements for
       <prot>Bcl-2</prot> / <prot>Bax</prot>  heterodimerization may be different from those for <prot>Bcl-2</prot>/<prot>Bcl-2</prot>
      homodimerization.
AD  - La Jolla Cancer Research Foundation, CA 92037.
