Hi All,<br><br><br>          The situation is complicated, and I am a first yesr PHD student. The data is not good (3A). Another protein in the same family has been published recently, so that we could use Molecular Replacement. <br>
<br>          Matthews&#39;s Coefficient suggested that there are two molecules in the asymmetric unit, however, we could only find one. It fits pretty well. And, we have a set of SeMet data. The two Se peaks are exactly on the sulfuers of the two Mets (that&#39;s very convincing, right?) Phaser and CNS gave us similar solutions. Anyway, then I started to build, and I found a problem: there&#39;s one DNA base pair missing in the complex (The DNA we used is longer than the model, so I needed to add back a few DNA base pairs. I need to add back two base pairs at each end, so between two symmates I expect electron density for four base pairs, right? But I only got density for three. I really couldn&#39;t understand.The only explaination I can come up with is that the DNA used in crystallography was wrong, but maybe someone could give me a few other possibilities.)<br>
<br>          We checked the space group again. Rmerge of P31 didn&#39;t seem better than P3121. The problem of missing density for DNA still exists... <br><br>          Maybe I haven&#39;t described my problem clearly... sorry for bottering... Any suggestion and comment are welcome. Thanks!<br>
<br><br><br>Xun Lu<br>Department of Molecular and Structral Biochemistry<br>North Carolina State University<br>