# Copyright (c) 2002-08 Peter Guntert. All rights reserved.
## 7MACROS: watsoncrick - CYANA macro
##
## Parameters: strand1=<integer range>        (required)
##             strand2=<integer range>        (required)
##             planar
##
## Creates restraints to enforce standard Watson-Crick-type pase pairing
## between two antiparallel DNA or RNA strands. The two strands must have the
## same length and continuous numbering. Optionally, additional planarity
## restraints can be added that restrain the interstrand C1'-C1' distances to
## 10.35-10.65 A for A-T and 10.6-10.9 A for C-G base pairs.

var info echo i i1 i2 j k l n

syntax $macro:strand1=@ii strand2=@ii planar

info:=none; echo:=off
if (strand1(2)-strand1(1).ne.strand2(2)-strand2(1)) \
  error "The two strands have not the same length."
i1=irnum(strand1(1)); i2=irnum(strand2(2))
n=0
do i strand1(1) strand1(2)
  j=irnum(i); k=i2-(j-i1)
  if (rnam(j).eq.'CYT' .or. rnam(j).eq.'RCYT' .or. \
      rnam(j).eq.'THY' .or. rnam(j).eq.'URA') then
    l=j; j=k; k=l
  end if
  if ((rnam(j).eq.'GUA' .or. rnam(j).eq.'RGUA') .and. \
      (rnam(k).eq.'CYT' .or. rnam(k).eq.'RCYT')) then
    n=n+1
    hbond H21 $rnum(j) O2  $rnum(k)
    hbond H1  $rnum(j) N3  $rnum(k)
    hbond O6  $rnum(j) H41 $rnum(k)
    if (planar) then
      distance make "C1\' $rnum(j)" "C1\' $rnum(k)" lol=10.6 upl=10.9
    end if
  else if ((rnam(j).eq.'ADE' .or. rnam(j).eq.'RADE') .and. \
           (rnam(k).eq.'THY' .or. rnam(k).eq.'URA')) then
    n=n+1
    hbond N1  $rnum(j) H3  $rnum(k)
    hbond H61 $rnum(j) O4  $rnum(k)
    if (planar) then
      distance make "C1\' $rnum(j)" "C1\' $rnum(k)" lol=10.35 upl=10.65
    end if
  end if
end do
unset info
if (planar) then
  print "    H-bond and planarity restraints for $n Watson-Crick base pairs added."
else
  print "    Hydrogen bond restraints for $n Watson-Crick base pairs added."
end if