[ccp4bb] Fwd: [ccp4bb] electron density slabs

[Poul Nissen]

This could be due to biscuit contamination of your protein - did you eat cake before setting up your crystallisation drops? Alternatively it could be a Fourier ripple - a very strong 5.4 Å resolution 00l reflection which is not correct Poul Begin forwarded message: From: hayato Jumonji <hay.jumo...@gmail.com> Date: 8. sep 2009 11.37.07 GMT+02:00 To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] electron density slabs Reply-To: hayato Jumonji <hay.jumo...@gmail.com> Dear all, I've phased 3 wavelength SeMet dataset with SHELX and the resulting mtz on Coot  shows ~5.4 A apart slabs in water channel. I've captured part of the electron density at 0.4sigma. The slabs appear through out the electron density and parallel to AB plane (space group P21212). Most of the electron density in the protein region looks good. But about 30% of the protein region is affected by this regular noise and appeared choppy. Although the protein region is still choppy, I do not see the slabs on another dataset. Could anyone suggest where I am getting this noise and how to avoid it ? Thanks in advance.