Some terms on plasmid replication control?

[pharmnmr]

I'm trying to study plasmid replication control. 
While I was reading a paper, I met some biological terms unfamiliar to
me.

plus origin of replication
minus origin of replication
countertranscript RNA(ctRNA) - Is it different from antisense RNA?

Could you tell me meaning of above terms or 
references on plasmid replication mechanism & control?
Additionally I'll appreciate to you 
if you tell me what news groups are involved with this subject.
Thank you.