Dear Morris,
1. I do not believe that it is lacZ that causes problems.
2. I have tried several preparation methods for DNA to be injected.
Minipreps which include and RNase treatment have never worked for me,
omitting the RNase helps. Significantly better is a Qiagen prep (obviously,
you get rid of the RNase on the column) or a CsCl prep. Similar results
were obtained by other people in our lab.
These observations are based on 70+ injections.
Good luck
Ralf Baumeister
Ruvkun lab
Mass. General Hospital
