Subject: 2 different mRNA sizes for one gene

I have noticed that some genes, such as those for collagen
types 1 and 3, produce two mRNA bands of different sizes on
northern blots.  This is well documented in research 
publications, but no paper has discussed the significance of
the two distinct mRNA products derived from a single gene.
The double mRNA is detected regardless if the nucleic acids 
were derived from total RNA or purified mRNA thereby 
eliminating the possibility of detecting homologous nuclear
RNA (hnRNA)

My question is: are both of the RNA species detected true
messenger RNA? Or is one of them (presumably the one with 
higher molecular weight)an unprocessed, or immature, mRNA
that undergoes further processing into a more translatable
mRNA?

Thanks for your help,

Richard Isbrucker

Re:2 different mRNA sizes for one gene