DNA isolation kits - Molecular Biology

I am trying to compare two different genomic DNA isolation kits. One involves adding SE buffer, lysozyme solution, RNase solution, SD sulphate and proteinase K then icubation at 37 C for 30 min. The other method is purgene kit for isolating buccal cells which involves cell lysis solution, RNase treatment, protein precipitation and then placing tubes in ice bath for 5 minutes.

Why in the 1st method is it incubated at 37 C and then in 2nd method placed in ice bath?

Thanks

QUOTE (Sarah_30 @ Nov 25 2006, 11:07 AM)

I am trying to compare two different genomic DNA isolation kits. One involves adding SE buffer, lysozyme solution, RNase solution, SD sulphate and proteinase K then icubation at 37 C for 30 min. The other method is purgene kit for isolating buccal cells which involves cell lysis solution, RNase treatment, protein precipitation and then placing tubes in ice bath for 5 minutes.

Why in the 1st method is it incubated at 37 C and then in 2nd method placed in ice bath?

Thanks

It looks to me that the 37 degree step is meant to allow the proteinase K to degrade the protein in the sample.

It looks like the second kit precipitates the proteins, instead of degrading them.

Would that make sense?

Yes, so precipitation of proteins can only take place at low temps then?

Not sure about the answer for your question. Typically lower temp tend to facilitate precipitation process, but not absolutely needed. You can also put it this way: protease K needs 37C to act fast.

DNA isolation kits - (Nov/25/2006 )