Cloning GFP into M13 vector?

[Brooks Robey]

Your problem may not be specific for GFP but may reflect a more general 
problem with subcloning with blunt-ended PCR products: Is your PCR 
product generated using Taq polymerase? If so, you might consider 
polishing your blunt-ends before cloning into M13, as this has been show 
by several investigators to improve ligation efficiency (I can dig up 
references if you desire), presumably because Tag has a nasty habit of 
tacking on an EXTRA nucleotide residue on the end . . .