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Medizin - Open Access LMU - Teil 05/22 Podcast
Location, transcripts, and translation products

Location, transcripts, and translation products

Medizin - Open Access LMU - Teil 05/22 vor 39 Jahren

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Cloned genomic fragments from the region (0.769 to 0.818 map units)
coding for immediate-early (IE) transcripts of murine
cytomegalovirus (MCMV) were used to analyze the physical
organization of this region, the direction of transcription, and
the proteins synthesized in vitro. Three IE transcription units
could be identified. From IE coding region 1 (ie1; 0.781 to 0.796
map units) a dominant 2.75-kilobase (kb) RNA was transcribed from
right to left on the prototype arrangement of the MCMV genome which
directed the synthesis of an 89,000-molecular-weight polypeptide
(89K polypeptide), the major IE protein. This phosphoprotein (pp89)
has been shown to be active in the regulation of transcription.
Upstream of ie1 and separated by the MCMV enhancer sequence was a
second IE coding region, ie2, which was mapped at 0.803 to 0.817
map units. From ie2 a 1.75-kb RNA of moderate abundance was
transcribed in the direction opposite to that of the ie1 RNA. After
hybrid selection of the ie2 transcript, a 43,000-molecular-weight
translation product was detected. A third coding region, ie3, was
located directly downstream of ie1 (0.773 to 0.781 map units). The
series of RNAs with low abundance, terminating in ie3, probably
used the ie1 transcription start site and ranged from 1.0 to 5.1 kb
in size. The 5.1-kb RNA apparently represents the nonspliced
transcript from both coding regions ie1 and ie3. A 15K polypeptide
was translated in vitro from RNA that was hybrid selected by ie3
sequences. Immunoprecipitation with monoclonal antibody revealed
that 31K to 67K polypeptides were related to pp89. Some of these
proteins were translated from RNAs that were smaller than 2.75 kb.
Polypeptides related to pp89 were also synthesized in vivo. Because
polypeptides unrelated to pp89 that were translated from RNA that
was selected by ie2 and ie3 sequences were not immunoprecipitated
by murine antisera, we assumed that the amount of these proteins
synthesized in vivo during infection was probably very low