Lab reports should be around 1-full page in length, lines single-spaced, and in a 12-point Times New Roman font. Use standard, grammatically correct English, and a narrative in past-progressive tense. Work is to be completed individually and working together is not permitted. All work is to be in your own words.
 The following sections should be included: 
1. Title. 
2. Summary of the work performed (half-page). 
3. Results obtained (quarter-page). 
4. Discussion (quarter-page).DNA UPTAKE DURING BACTERIAL
Inês Chen and David Dubnau

Naturally competent bacteria are able to take up exogenous DNA and undergo genetic
transformation. The transport of DNA from the extracellular milieu into the cytoplasm is a complex
process, and requires proteins that are related to those involved in the assembly of type IV pili and
type II secretion systems, as well as a DNA translocase complex at the cytoplasmic membrane.
Here, we will review the current knowledge of DNA transport during transformation.


Bacteria can acquire new genetic information by three
means: conjugation, transduction and transformation.
During conjugation, DNA is transferred directly from
one organism to another, whereas in transduction, the
DNA is carried by bacteriophages. Transformation
involves the acquisition of naked DNA from the extra-
cellular environment (BOX 1), and genetic competence is
the ability to undergo transformation. Early experiments
on transformation showed that DNA is the genetic
material (BOX 2).

Since the advent of recombinant DNA technology,
biologists have transformed Escherichia coli, the ‘work-
horse’ of molecular biology, using procedures that alter
the permeability of the cell membrane (for example,
using calcium or electroporation), such that DNA can
be introduced to the bacterial cell. By contrast, in this
review we will discuss natural transformation, in which
specialized bacterial proteins are responsible for the
uptake and processing of DNA. At least 40 bacterial
species, distributed through all taxonomic groups, are
known to be naturally transformable1. In most of these
species, genetic competence is a transient physiological
state, the development of which is tightly controlled by
organism-specific processes, including quorum sensing
and nutritional signals2–4. It is therefore possible that
many more species are competent for transformation,
but the conditions in which they develop competence
are still unknown5.

Transporting DNA from the extracellular milieu
into the cytosolic compartment is a complex task.
The incoming DNA must cross the outer membrane
(in Gram-negative bacteria), the cell wall and the

cytoplasmic membrane. The outer membrane of Gram-
negative bacteria represents an extra barrier for the
DNA that is absent from Gram-positive bacteria, and
this lends confusion to the term ‘uptake’. Uptake is
defined operationally as the conversion of exogenous,
DNase-sensitive DNA into a DNase-protected state. In
Gram-negative bacteria, this protection can be
achieved by crossing the outer membrane; by contrast,
in Gram-positive bacteria, DNA uptake is synonymous
with passage across the cytoplasmic membrane. Only
one strand of the DNA molecule is effectively trans-
ported into the cytoplasm; the other strand is degraded
into nucleotides, which are released into the extracellular
environment (in Gram-positive bacteria) or presumably
into the periplasmic space (in Gram-negative bacteria).


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