(add-to-list 'org-latex-classes
             '("portrait_poster_a0"
               "\\documentclass[t]{beamer}
           \\usepackage[orientation=portrait,size=a0,scale=1.2,debug]{beamerposter}
           \\usepackage[absolute,overlay]{textpos}
[NO-DEFAULT-PACKAGES]
[PACKAGES]
[EXTRA]"
     ("\\section{%s}" . "\\section*{%s}")
     ("\\subsection{%s}" . "\\subsection*{%s}")
     ("\\subsubsection{%s}" . "\\subsubsection*{%s}")))