HI
I had same a problem. Now everyting is normal.
you can wash PCR tubes in 5% HCl and you can work in cabine

So far we've found that our main source of PCR contamination is the people themselves.  If a person handles amplified PCR product, that product gets all over them, even if there is extreme care taken.  I believe it is just the aerosol of the PCR product that gets on the face, hair, etc.

If the person then goes on to prepare subsequent PCR reactions, there is a high liklihood that some of the wells will be contaminated with previous PCR products.

The workaround we've found to this is to simply set up all pre-PCR steps before handling any post-PCR product. 

It seems that a shower and a clean set of clothes is enough to prevent the contamination problem.  Of course, this is only practical on a daily basis.

And yes, we do have different sets of lab coats.

I have a question regarding false positive PCR results and I'm desparate for suggestions:
I'm cloning this 7.5 kb PCR product with RE digestion site added at the both ends in primers: KpnI at the 5' and XhoI at the 3'. After PCR, I TA cloned the product into TOPO vector and got the right one and sequenced the whole
insert. Next, I'm trying to cut the insert out with KpnI and XhoI, then put that into my 9.2 kb expression vector that is also digested by KpnI and XhoI and dephosphorylated. Both inserts and vectors are gel purified. After ligation either at rm for 5min or 16c for 2h, I did chemical transformation of Top10 competent cells, and got about 3 fold number of colonies comparing to vector alone. And when doing PCR colonie screening, all the 12 colonies I picked gave me the PCR product of the right size as the positive control, although some do contain a smaller second band. The negative control (no DNA) didn't show anything. I thought I got it. But miniprep of 2 colonies only gave 1 single band upon KpnI and XhoI digestion. I'm pretty sure the enzymes work well. Also, the linearized fragment is smaller than the expected (7.5+9.2) 16 kb, instead, it's about the size of the insert plus the Topo vector.However, no insert was cut out. If it's due to contamination, why my negative control is negative? If it's due to bad enzyme, why the size is wrong? Any other explanations? BTW, my expression vector has different antibiotics resistances from TOPO vector. Any suggestions?

Hi, everybody. Please take a look at my last HCV RT-PCR gel. I.v got many unspecific bands which I'v never had before. Is it possible that a so called specific primer pairs bond to other DNA rather than HCV cDNA. Is it a contamination disaster?

Thanks

Omar.14--
Give us more details, such as organism etc.

Try using a different set of tips, reagents etc when setting up your negative control - perhaps even a seperate master mix - never rule of anything when looking for contamination. We once had contamination because our pippete tips, when autoclaved used to "collect" biological matter at the tip - and this caused contamination...

Show a gel please!