1.Ans :

                                                                
TI: DNA recognition by beta-sheets in the Arc repressor-operator 
    crystal structure.
AU: Raumann-BE; Rould-MA;Pabo-CO; Sauer-RT
AD: Department of Biology, Massachusetts Institute of Technology,
    Cambridge 02139.
SO: Nature. 1994 Feb 24; 367(6465): 754-7

AB:  Transcription of  the ant  gene during  lytic growth  of 

bacteriophage P22 (ref. 1) is regulated by the cooperative binding 

of two Arc repressor dimers to  a 21-base-pair operator site. Here 

we report the  co-crystal structure of this  Arc tetramer-operator 

complex at 2.6 A resolution. As expected from genetic and structural

studies  and from  the co-crystal  structure of the  homologous 

Escherichia coli MetJ repressor, each Arc dimer uses an antiparallel 

beta-sheet to recognize bases in the major groove. However, the Arc 

and MetJ complexes differ in several important ways: the beta-sheet-DNA 

interactions of Arc are far less symmetrical; DNA binding by Arc is 

accompanied by important conformational changes in the beta-sheet; 

and Arc uses a different part of its protein surface for dimer-dimer 

interactions.

2.Ans :

The paper of Smith and Sauer. (In PDF format)