Unusual electrophoretic mobility of maize Hrgp mRNA

Hybridisation bands of mobility lower than expected appear in RNA blot analysis performed using total maize RNA hybridised with an hydroxyproline-rich glycoprotein (HRGP) cDNA probe. This behaviour has previously been observed and some authors have proposed that these bands could be transcripts of genes coding for highly similar genes. However, other data indicate that a single gene coding for HRGP exists in the maize genome. Here, we show that some of the mRNA molecules hybridising with the Hrgp probe migrate in agarose gel electrophoresis at a lower velocity than expected. The relative intensity of these low-mobility bands depends on the abundance of the Hrgp mRNA molecules loaded in the electrophoresis gels, a result confirmed by using two-dimensional gel electrophoresis. We propose that these hybridisation bands may be the product of different secondary structures or multimers of the 1.5-kb Hrgp mRNA probably due to high G+C content and the highly repetitive sequence of these molecules.