Protein extraction and isolectric focusing - (Mar/25/2013 )

So I am doing my university junior research project which required to prepare and compare 2D gels containing proteins extracted from a bacterium (Sinorhizobium meliloti). These gels had the proteins seperated by isoelectric focusing. Now, some of the gels I had prepared had "train spots" on them and I am slightly confused by why they actually form. I know that these "train spots" form as a result of post-translational modifications but is that the only reason? Is there any association between their similar molecular weights & their differnt pIs that cause them to form next to one another? Also what about the phenomenon where protein spots of different molecular weight match the predicted proteins (eg: they match to tubulin or an ATPase). I am confused as to what is happening there.

Any help clarifying the matter would be much appreciated thanks.

So I am doing my university junior research project which required to prepare and compare 2D gels containing proteins extracted from a bacterium (Sinorhizobium meliloti). These gels had the proteins seperated by isoelectric focusing. Now, some of the gels I had prepared had "train spots" on them and I am slightly confused by why they actually form. I know that these "train spots" form as a result of post-translational modifications but is that the only reason? Is there any association between their similar molecular weights & their differnt pIs that cause them to form next to one another? Also what about the phenomenon where protein spots of different molecular weight match the predicted proteins (eg: they match to tubulin or an ATPase). I am confused as to what is happening there.

Any help clarifying the matter would be much appreciated thanks.