<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; ">Dear all,<DIV><BR class="khtml-block-placeholder"></DIV><DIV>I would like some advice on how to combine MAD and native in SHARP. I've never done this before. I've tried following the instructions in the manual, with little success. Two scenarios are described there:</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>1) Use SeMet in the derivative and S-Met in the native</DIV><DIV>2) Use (Se-S)Met in the derivative and nothing in the native.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>In both cases I use the peak wavelength of the MAD data set as reference. I have a set of 11 Se positions from a simple MAD refinement. The orthorhombic cell dimensions are 75.47 128.94 175.98 for SeMet and 74.95 127.25 175.21 for native. The MAD data go to 2.8Ĺ and native to 2.3Ĺ. SCALEIT gives an isomorphous R-factor of 17%, which is maybe a bit on the high side for Se...</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>In scenario 1, if I let the occupancies of the S atoms in the native vary then they fluctuate wildly, as do the Se occupancies in the derivative. If I fix the S occupancies to 1.0 then nothing much happens to the Se occupancies, but the NISO_BGLO parameter for native goes up to 4.4 and the native contributes nothing to the phasing. Am I refining incorrectly or are the data just very non-isomorphous? There is after all a 1.7Ĺ difference in the b dimension...</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>In scenario 2 I have not gotten very far because I have no idea what to put in as f' and f'' for a Se-S atom. Any suggestions? </DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>I would like to know generally speaking what is the correct course of action for combining native with MAD and what experiences people have had in the past.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Thanks</DIV><DIV>Derek</DIV><DIV><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Courier" size="3" style="font: 12.0px Courier">--</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Courier" size="3" style="font: 12.0px Courier">Derek Logan <SPAN class="Apple-converted-space"> </SPAN>tel: +46 46 222 1443</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Courier" size="3" style="font: 12.0px Courier">Molecular Biophysics<SPAN class="Apple-converted-space"> </SPAN>fax: +46 46 222 4692<SPAN class="Apple-converted-space"><SPAN class="Apple-converted-tab"> </SPAN></SPAN></FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Courier" size="3" style="font: 12.0px Courier">Lund University</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Courier" size="3" style="font: 12.0px Courier">Box 124, Lund, Sweden</FONT></P> </DIV><BR></BODY></HTML>