BackgroundThere is a steadily increasing demand for producinghigher yields of biopharmaceuticals as recombinant pro-teins, and it is anticipated that this will further expandduring the next decades. Among the most frequent pro-teins produced are growth factors, monoclonal antibo-dies, hormones and blood coagulation factors.The production of recombinant proteins can be per-formed in expression systems derived from bacteria,yeast, plants, insects or mammals. Prokaryotic cellsdivide rapidly, making it possible to produce high yieldsof the protein at low costs. They are, however, normallynot able to perform post-translational modification ofproteins, which, for those of mammalian origin, is essen-tial to ensure stability, proper folding and assembly andthus biological activity. Mammalian cells, on the otherhand, confer post-translational modification. Unfortu-nately their cultivation is cost expensive and time con-suming, they grow slower, are more sensitive tocontamination and produce lower protein yields thantheir prokaryotic counterparts. Despite this, 60-70% ofall recombinant proteins used in therapeutics are pro-duced in mammalian cells. Yield improvement in mam-malian systems is currently an area of major industrialimportance [1].To achieve this, two main strategies have been used:(1) optimising the components of the vector containingthe gene of interest, and (2) optimising cell growth andselection. Optimisation of the vector by genetic engi-neering has mainly focused on increasing the efficiencyby which the gene is transcribed. The concept beingthat a high level of transcription would ultimately leadto a higher protein yield due to increased availability ofmRNA for translation. Vector design, the chromosomalenvironment of the plasmid integrated in the host gen-ome and plasmid copy number, are among the para-meters that can contribute to transcription efficiency.An increased level of mRNA coding for any secretedprotein of interest, however, will only be beneficial if thetranscript is correctly transported to the endoplasmicreticulum and then effectively translated. This area hashitherto been largely neglected.Efficient mRNA processingUniTargetingResearch AS is now developing and com-mercialising tools to optimise protein synthesis andsecretion, by ensuring that the mRNA encoding the pro-tein of interest is efficiently processed. This has proved tobe heavily dependent on the presence of specific genetictargeting elements, namely a selected signal sequence(SS) in combination with appropriate 5’ and 3’ untrans-lated regions (5’ and 3’UTRs). Our focus is currently onthe SS, which is translated into the signal peptide (SP).Earlier we observed a competition between a selectedSS and the 3’UTR in mediating mRNA targeting to dis-tinct classes of polysomes [2]. We therefore investigatedthe effect of different SPs derived from mammaliansecretory proteins on the synthesis/secretion of Gaussiaprinceps (a marine copepod) luciferase (Gluc) used as areporter protein [3]. The results showed that the choiceof SP had a major impact on synthesis/secretion of Glucin CHO cells. Contrary to what was expected the SP ofalbumin was extremely inefficient (<5%) in Gluc produc-tion when compared to that obtained using the SPderivedfromthemarineorganism.Similarresultswereobtained when liver cells were used instead of CHO